In reading old newspapers, archives, and Government records, I have found many references to William Sykes. It is hard to include them all in essay form so I am listing them below.

From ‘'The Sydney Gazette'
1. A letter for Mr W. Sykes is waiting to be picked up. 8th October 1810 and 28th January 1815.
2. William Sykes supplied meat to the Government Stores in Parramatta. 14th June 1817, 24th April 1819, 1st January 1820.
3. William Sykes supplied wheat to the Government Stores. 20th January 1821.
4. William Sykes supplied wheat to the Government Stores. 3rd February 1821.
5. William Sykes supplied wheat to the Government Stores. 3rd March 1821.
6. William Sykes supplied wheat to Government Stores. 29th December 1821.

From Ship Indents, Archives of N.S.W., "Indents of Convicts Ships 1801-1814", page 219
William Sykes, from Middlesex, who arrived on the Fortune in 1806 with a sentence of 14 years, is granted his Absolute Pardon.

From "The Register of Absolute Pardons", page 33, No. 5, on 17th March 1810
William Sykes, from Middlesex, who arrived on the Fortune in 1806 with a sentence of 14 years, is granted his Absolute Pardon, by Governor Lachlan Macquarie.

From 'The Sydney Gazette', Saturday, 12th September 1812
"And such of the following persons as have executed the necessary Bonds, -are to attend, to receive the Cattle assigned to them on Thursday 15th October next, at the Government Stock yard, at the South Creek." Among the list of approx. 10 is William Sykes. It continues: "All those who have oxen approved must attend the Government Stock Yard at Parramatta on 22nd October as they cannot be distributed at the same time as the cows."

From 'The Sydney Gazette' on 14th July 1810
"If the undermentioned persons will make application at this office on Monday the 16th July inst, they will receive an order for such quantities of Cloth as they may be entitled to on account of wool delivered at the Factory at Parramatta.
"By Command of His Excellence, William Broughton, Acting Commissary." In the list: William Sykes.

From "The Harvard Index", on 2nd September 1822, Historical Records of Australia
"William Sykes (Appin) was amongst one hundred people who signed a letter to the Governor. It was a memorial from the Colonists about the danger they could see in using Spanish Dollars as payment for goods. They were fearful that there would be a great loss in exchange."

From 'The Australian' of 6th July 1832
"William Sykes (Appin) with 100 names signed an address to Capt. Meyrick, Thomas Meyrick Esq., Captain in His Majesty's 39th Regiment, Justice of Peace and Superintendent of Police for District of Aides, etc.
"Having heard that the 39th Regiment is shortly to leave this Colony for India and that you are about to retire from the arduous duties of your office as Superintendent of Police in these Districts, to proceed with that Regiment, we beg to assure you of our unfeigned regret at the circumstance of your departure from us.
"We sincerely wish you and your family every happiness which can be enjoyed by an upright, and impartial man."

From 'The Sydney Gazette' on Monday 13th August 1827
"These races will take place this day at 10 a.m. at which place there have been several horses in training for the occasion, but the first and principal Race will be between Mr Hammond's three year old Colt, and Mr Cullen's Favourite, 5 year old, for fifty pounds, the best of a two mile heat.
"The second Race will be between Mr Boon and Mr Sykes, for sweepstakes, and the third between Mr Patrick's Alpha, and Mr Lack's Omega.
"It is expected that these Races (being patronized by Authority) are likely to excite considerable interest from the heavy bets pending, arising out of the known Character, Blood and Ability of the several Horses, but especially the first entered."
I don't know if William rode this horse; he may have hired a jockey, as he was 54 years old. George, his son, may have ridden him as he was then 17 years old.
This Mr Boon very likely was Nathanial Boon of the Fisher's Ghost Trial.

From 'The Sydney Gazette', on 8th August 1828
An advertisement appeared as follows: "Two hundred and twenty Breeding Ewes and Lambs of the best Spanish Breed with two excellent Rams, the whole not exceeding 4 years old warranted sound, and in good condition.
"For further particulars apply: Mr William Sykes, District of Appin."
This advertisement was repeated in the Gazette on 11th August 1828 and 20th August 1828

From 'The Sydney Gazette' on Tuesday,21st April 1829
In the Supreme- Court column of the Gazette, there appeared this note:
"On Wednesday the 29th inst. at Campbell Town at 12 o'clock, the Sheriff will cause to be sold an excellent house, containing four rooms, weather board and shingled. The house is situated on the road side in the District of Appin, and is near the Estate of William Browne Esq., and the Farm of Patrick Gallagher; after which sundry articles of household furniture the whole the property of the above defendant, unless this Execution be previously satisfied."
This notice is repeated on Thursday, 23rd April 1829, Saturday, 25th April 1829, Tuesday,28th April 1829, and Thursday,30th April 1829.

In 'The Sydney Gazette' under Law Courts, this notice appears on 26th March 1829
"On Thursday the 2nd day of April next at 12 o'clock in the Market Place, Sydney, the Sheriff will cause to be sold a farm, containing 250 acres, 150 of which are cleared, and divided into 5 paddocks, all fenced in, there is also a good house and barn, and out houses, shingled and weather-boarded, and situated in the district of Appin, and adjoining Mr Broughton's Estate. This farm is well worthy the attention of any person desirous of settling in the Country.
"After which will be sold one hundred and thirty sheep in excellent condition, and well bred. Unless this execution be previously satisfied."
This was repeated in the Gazette on 28th March 1829, 31st March 1829 and 2nd April 1829.

On 4th April 1829, this appeared in 'The Sydney Gazette'
"On Monday the 13th inst. at one o'clock in Sydney Market, the Sheriff will cause to be sold that truly desirable farm situated in the District of Appin, being 130 acres of Land, bounded on the North East line of 55 chains, 50 links, adjoining part of Kennedy's farm on the East by a South line of 30 chains, on the South by a West line bounding Coss' farm to the Branch of the Nepean River, and on the West by that River, unless this Execution be previously satisfied."
This is repeated in the Gazette on Tuesday,7th April 1829 and 14th April 1829.

Reported in 'The Sydney Gazette', 5th February 1827, the famous Fisher's Ghost Trial
"George Worrall was indicted for the wilful murder of Frederick Fisher of Campbelltown, on 16th day of July last. The information charged the death to have been caused by sundry wounds inflicted on the skull with a stick.
"The Acting Attorney General W. H. Moore Esq., stated the case, and called Mr D. Cooper to give evidence, he was cross examined, and then William Sykes was called upon, as the second witness.
"William Sykes, said he knew the prisoner, and the deceased, he has had some conversation with the prisoner after the disappearance of the latter. The prisoner said he purchased of the deceased, a grant of 30 acres of land, a gig, and some horses for which he had a receipt. Mr Sykes said he had heard that a man named Talbot purchased one of the horses from the prisoner. The prisoner desired Mr Sykes, after his apprehension, to tell Talbot if any one came to enquire after a mare he had, to say he rented her for three months.
"Mr Sykes was then cross examined. He said: 'Can't say what might have been the prisoner's reason for desiring him to give the message to Talbot, but he suspected that the prisoner had sold him the horse which afterwards turned out to be the case'."

In R. Darling's Despatch, 1830, A 1208, page 918
"While surveying which road would be better, the Cowpastures or Razor-Back, the engineer thought a new line would be to advantage.
"On inspecting the Map it will be seen that the road near Lupton's has a remarkable turn, nearly at a right angle, which takes it through the Cowpastures District.
"The line we examined is a continuation of the road in a straight line beginning at this bend to the River Nepean, thence across (still mainly in a straight line) to the Cataract River at a pass near one of Sykes' farms, and from thence by easy line to Liverpool.
"The only difficulty he could see was the crossing of two rivers, but he said he thought bridges could be constructed without any very extraordinary quantity of labour.
"Signed T. L. Mitchell (Surveyor General), William Cordeaux, George Innes."

From Macquarie's Tour of N.S.W., October 1815 From "The Diary of Governor Macquarie"
"From Mr Kennedy's we proceeded to see the Farm of Mr Sykes, about half a mile further to the Southward, and at present the most Southern one in Appin. This man has with small means, made wonderful exertions having cleared and cultivated a large proportion of his Farm, and there is every appearance of his having an abundant crop of wheat this season. In consideration of Sykes' industry, I have promised him an addition of Seventy Acres, adjoining immediately his present one which will make his whole Farm 150 acres. Sykes' farm is supposed to be about 20 miles distant from the ground we departed from this morning, and we have at least ten miles to ride to our next ground or station at the Stone Quarry Creek in the Cowpastures, where all our Servants and Baggage proceeded this morning at the same time we set out for Appin.
"At 2 p.m. we set out from Sykes' farm on our return to the Cowpastures and crossing the River Nepean at Mr Riley's Farm." (See copy page 18.)

From N.S.W. Colonial Secretary, in Letters,28th October 1832
"William Sykes in debt for one cow £28 (to be paid in kind)."

From N.S.W. Returns 1819-1820, Biggs Appendix, page 113, Vol. 130
"William Sykes, married, ex-convict, intelligent, honest, sober and industrious."

From the Register for the County of Cumberland and Elsewhere No.2, 1810-1821
"Grant by Lachlan Macquarie, registered on 10th June 1815, for one shilling per year. Commence payment on 1()th June 1820. Name of property was 'Mount Britain'. Witness H. C. Antill and John Watts.
"This 80 acres: bounded on N. side by 40 chains of Broughton, Lachlan Vale Farm, bearing W. to S.W. angle of that farm. On the W. by a S. line of 21 chains, on the South by an East line of 40 chains, on the E. by a N. line of 21 chains, to Broughton's farm.
"Condition not to sell or abnegate same for five years: to cultivate 18 acres reserving the right to a public road, and all such timber as may be deemed fit for Naval purposes.