Freedom of information would be the way to go . I've only had experience with vic roads but you should be able to do it nationally . Usually I contact Vic roads first to see if they have any record of the vehicle , you may have to get them to look in there archives but usually this involves ringing several time to get someone that's willing to help. If there is a record they only can confirm details , they cant give you any details . Even if you don't find records you can still apply under the FOI for information . You need to be specific on what you want to know , don't just apply for any record . List what you want to know . Eg previous rego number or engine number or even previous owners .