http://www.ereplacementparts.com/dewalt-dw936-type-cordless-saw-parts-c-1009_2446_3855.html
Thats where you can get the parts. As for how to replace the brushes, it looks like you probably need to take the entire thing apart.
But thats a little strange, normally something thats not very old doesnt need its brushes replaced. I find things that are around 15-20+ years and have been used alot need the brushes replaced. It sounds like there might be some other issue.
But they are cheap and it wont hurt to replace them anyways.
[[Topic:DeWalt DW936]]
You can follow those guide on how to get it apart.