Brake pads are readily available from Bendix and others - same as (Oz) GTR / 300ZX - DB1170 front, DB1220 rear.
Air filters are same as earlier (R30 / R31) Skylines, or Commodore. Oil filters are same as earlier Skylines.
Thermostat - I bought one for a VL-Turbo for my RB20DET. Even came in a nice Nissan box.
Any other parts, Nissan dealer can get them in from Japan - usually about 2 weeks delivery.
Worst case, you can try any of the numerous import wreckers.