Help to find my Convict John Croxford

Hi,
My ancestors are Croxford's from Aston Rowant, Lewknor, Chinnor areas. Recently I found a John Croxford who was tried on the 2 July 1817 for violent theft and highway robbery and found guilty, sentenced to death, which must have been changed to life and transportation to Australia. He was 27 when convicted. He arrived in NSW Australia aboard the Lady Castlereagh in 1818. I have found several pieces of information about his life in Australia. He was given permission to marry Mary Burchun on 15th Sept 1832 when he was 42. He was Pardoned on the 20 Nov 1837. On a Ticket of leave, ( this was given to convicts to allow them to work for private individuals ), it states his native place as being Kingston ( I take this to be Kingston Blount ) and his trade was a sawyer. Because of the information that I have, I think his date of birth would have been about 1790, but I have been unable to find a record of his birth or baptism. I would love to find out who his parents were so that I can fit him into my tree. Can anyone help or maybe point me in the right direction.