Wreckers pretty much are useless for these cars, especially any in adelaide.
For secondhand parts, this forum is probably your best bet. There's always a few cars being wrecked, and prices are usually pretty good.
Beyond that, the forum sponsors can usually track down most of the bigger stuff for a good deal.
Twosrus have a pretty good range of new miscellaneous parts. Shipping is a bit more from the states, but prices are still good. I got new T-top seals, door handles, etc.
Amayama (+ Toyodiy) or Lithia Toyota can get you pretty much any OEM part if you can't source it elsewhere.
As for the gearbox, I'd be inclined to look for a replacement, so long as its from a trustworthy source. I've got the Gen3 box in mine, as it has better synchros I think, and LSD.