His death cert was in NSW. You can buy this online by credit card:
ww.bdm.nsw.gov.au/familyHistory/search.htm

Registration Number Last Name Given Name(s) Father's Given Name(s) Mother's Given Name(s) District
13255/1975 / CORKILL / AUBREY CLARION CLIFFORD / LEWIS WILLIAM / MATILDA

This means he died in 1975. His cert should give more information about his parents and whether he was born in NSW or elsewhere, plus his exact age and a lot of other information. From this info you can find his parents' marriage cert, and his birth, etc. etc. - going back step by step.

Sue