All the Athearn motor brushes and springs work with all the BB "Jet" motors.. Yeah and I would agree this isn't something you'll find in a hardware store. You can call or email Athearn to order them. The other option is to pick up an Athearn junker at a train show with it's motor intact.
Jay
C-415 Build: https://imageshack.com/a/tShC/1
Other builds: https://imageshack.com/my/albums
Don't know which motors these fit, but: http://www.athearn.com/Search/Default.aspx?CatId=THCR&SearchTerm=brush
Edit: Here's a part diagram for the Jet motor: http://www.hoseeker.org/assemblyexplosionAthearn/athearnmotors8400085000.jpg
Have you tried Athearn's Parts Department? They have a very extensive listing of spare parts on their web site.
http://www.athearn.com and then click on "Parts" near the top of the page.
I doubt that any local hardware store is going to have anything close to fitting an Athearn motor.
Anybody have an idea about what can be used from the local hardware store (etc) to make substitute motor brushes for athearn grey (jet) and gold (1980s, say) motors? And/or a source for tiny springs (for same) as well?
Mike