New South Wales newspaper archives 1955-1995
To apply for a legal name change you have to be an Australian citizen so I suggest that you check naturalisation records at http://www.naa.gov.au/collection/using/search/ (search as a guest)
The Department of Immigration and Citizenship may be able to offer advice if you are trying to find someone
Most personal information from that time period is not available to the general public.
I can confirm that the naturalisation records are not available from the National Archives of Australia until they reach the open access period (see fact sheet 10). Currently, records that were created during or before 1981 are being released for public access. From January 2012 we will begin releasing records created before or during 1983.
If the people you are interested in were naturalised before 1981, you can submit a reference inquiry using the form at http://naa.gov.au/collection/forms/imm-inquiry.aspx. Otherwise, if they were naturalised during or before 1983, you can submit a reference inquiry for those records during 2012 (using the previous link).