There aren't any good LFS in DC that I know of, but there are a couple in the surrounding area. You can buy Eheim stuff at all local Petco and Petsmart locations that I have ever been to. There is only one Petco in the city and zero Petsmart. But there are tons of Petcos and Petsmarts in the surrounding 'burbs. Are you riding the metro or will you have access to a car? Let me know and I'll try to help as much as I can.
Fraternity of Dirt #30 - SunSun Pimp Club #20 - Eheim Pimp Club #412