Google LarryLugs.com, he sells aluminum boggie rollers and other track parts aftermarket that are better and cheaper than the OEM. Putting this thread in the Cat-apilliar section might get more hits.
For rebuilt drive motors, you might want to contact Machinery Parts Warehouse. They have a great stock and good prices.
I got my track parts from Fortis Tracks last year. Reliable and fairly priced. Check them out.