The old NSW Dept of Fair Trading REVS check pretty much had to be done over the phone - and even then, they were pretty retarded ("I know you said it has no engine, but I NEED an engine number" - so I'd just give them the number 123456).
AFAIK, it's closed down now, and it's been moved over to the nationwide PPSR.
And that the PPSR is hopeless for reporting whether something is stolen...
Ring the cops. If you ave the slightest reason to think its come from interstate, then ring the cops in the other state(s) too.
Also check stolendirtbikes.com(.au?) - its not sure fire, but it helps.
Side note: a mate bought a KDX200 but couldn't do the online check because the website was down. Seller seemed legit, but the bike was stolen... It worked out OK for him (he bought it off the insurance company), but it cost him an extra $500 and a truckload of stress and hassle).