if you don't need it to be road registered, find a shell that cannot be registered (writeoff, failed compliance, parts import etc) and build it up. That way you start from scratch. That's if you don't have access to a CAMS accredited license that makes you eligible for a race import.
However if you are eligible for a race import then you can buy GTR's that are in various stages of modification. From:
http://www.j-spec.com.au/list/6600
to
http://www.j-spec.com.au/list/3340
to
http://www.j-spec.com.au/list/6377
(just using race imports on our mailing list as examples). There's heaps more modified ones out there. As a race import it dosen't have to meet the strict rules for SEVS so you can actually hunt around for some real bargains in japan.