Hi David
I don't know if there is a quicker way than the way I did it but, depending on your relatives dates of birth, they could be on the 1901 census - I may be putting my foot in it not knowing how old you are!! Anyway, once I got the info from the census this told me roughly how old the relative was and then there are a few websites where you can find out the quarter the person was born in a particular year and then send off for their birth, marriage or death certificate from the Government Records Office. I am assuming that they will send out to Australia, but not too sure.
Ann

PS It is a game of patience!!