You probably won't find a place that will sell you just the brushes or repair the window motor for you.
However, my local Advance Auto Parts sells reconditioned J30 window motors for about $55 (provided you give them your old one as core).
I've installed two of these reconditioned (rebuilt) window motors in my J30 and have not had a problem with them. It's been over two years since I installed the first of the two.
They're also guaranteed for as long as you own the car. Not a bad deal. Even if it were to go bad, just take it back and get another one.
BTW - Welcome to NICO. Make sure you check out my J30 website when you have a chance.
http://www.fuzzycats.com/j30.htm
Carlos