Looking for the Migration of John Thomas Bowers to Australia Pre 1868

John Thomas BOWERS was the [unconfirmed] husband of Priscilla (aka Martha) PITHERS who supposedly married at Glebe, Sydney, New South Wales, Australia in 1868. As I can find no birth for him in Australia I presume he emigrated to Australia. Has anyone found his birth date - thought to be around 1845 and the place.

Cheers
Maddy in New Zealand