DC:

CityBikes in Adams Morgan is the only place to get track parts in DC. See Shawn.

The Pro Shop in Georgetown caters mostly to the roadie set, but they have a lot of nice stuff. They have a good tire selection. You can find one or two track parts there, like clips, but that's about it. I go there sometimes because I like the people and the shop.

Sadly that's it for DC proper. Someone else can address the suburbs (like college park, if it hasn't already been mentioned).