There is a Genuine Parts thread in Tech Articles that has some numbers, has the rear seal number at least. It will be updated again sometime.
Most service and replacement parts like seals and bearings will be alot cheaper at Burson or Repco rather than Toyota. But if you go to Burson, you just have to say you want a diff seal for a old Celica and stuff like that. All 4A rear main seals should be the same, or similar enough. The tailshaft centre bearing from Toyota will cost heaps, maybe $300?