John Sharp Where Did He Come from

Originally thought to be a family legend but seems to be true, that
John Sharp married an aboriginal woman and had a family, including a son named Richard whose line I am trying to follow.
Very little is known date wise beyond John may have been born about 1810, and may have died about 1884.
Australian records contain a lot of 'unknowns' and this appears to be one of them.
I have looked at the lists of convicts sent to Australia and there are up to ten possibles.
Any help would be really appreciated.