There are a lot of different places people buy parts. The best thing to do is to use the search feature for the parts you are looking for on this site. For instance putting "bearings" in the search box should lead you to some threads that will inform you where they bought theirs from ie Buffalo Bearings for axle bearings or Recreative Industries (RI) for the T-20 inner bearings. If your machine does not have the factory engine or has a techumseh in it you will have to do some leg work to find engine parts. Allot of parts for your machine should be available from RI out of Buffalo though. It's the manufacturer and some parts are only available from there, however, its not a huge plant and they source parts too, so if you can figure out where they get them from you can save a buck here and there.
Richards Relics can be pricey. It is a one stop shop and can have specialty items that are hard to source but beware of inferior parts and new T-20 bands are only $5 more from RI than buying the referbed bands from Richard
l like to buy stuff and no I don't do payments!