I know you used to be able to go to the RTA in N.S.W with a rego of a vehicle you were chasing, write a note (I think it was a particular form) and they (RTA) would foreward that note to the current registered owner. It was then up to the contacted person if they wanted to respond to you or not. Might work for chasis number, maybe not, the RTA worker would have to dig up the rego to get current owner, might be too hard basket stuff.