The quickest way to find an Australian .au domain name owner is to use the recover password tool at http://www.ausregistry.com.au/tools/recover-password.
The AusRegistry.com.au recover password tool can also be used to help transfer Australian domain names between registrars.
Ausregistry.com.au also provides the raw list of domain which ‘drop’ each day http://www.ausregistry.com.au/tools/official-domain-name-drop or those domains which someone has forgotten to renew, which happens a lot, or genuinely no longer uses or wants the domain.