Salt and sundry at union market has bitters as well.

Magruders in Chevy Chase circle has a lot, fwiw.

OP here - in case anyone wants to know, I took the lazy route and ordered from Amazon!

Not sure where to buy, but I like Fee Brothers. Their "standard" type flavor is quite different than Angostura, but still very appropriate for the same uses, like Manhattans.

I wanted to get my dad a small bottle of specialty bitters for his birthday - which flavor would be most versatile for different cocktails and where could I find bitters in the Bethesda/Rockville area?