It's obviously much easier to get stuff for the 2Jz, but .....
You can get decats in the UK (but in the end it's just a pipe, so any exhaust fabricator should be able to make one).
Dump pipes from Oz.
You can make a cold air intake (otherwise known as a BFI -- Big F**** Intake) or buy one.
gamer (who posts here and on TIF) and Bedlam (on LSOC) have single conversions.
There are quite a few cars running decent power with the twin turbo set up, either the original ceramics, hybrids, or aftermarket kits
Useful links
LSOC http://www.lexusclub.co.uk/
TIF http://www.toyotaimportsforum.co.uk/
ALSC http://www.alsc.aus.as
Planet Soarer (BFI) http://planetsoarer.com/
mkiiisupra.net http://www.mkiiisupra.net/ (the 1JZ was also used in the MkIII)