Hi Mark,
I grew up in DC, but it has been several years since I've been back.
You know of Georgetown Tobacco on M Street. the other shop in the District that I am/was aware of is/was Curtis Draper's on 14th st. near the white house - between F and G streets.
Across the Md. line in Bethesda is J.B. Sims. I forget the address, but you could google them.
I know there are some participants on ASP from the area, so you might want to post your question there as well.
TC