Dan Gearino has posted a list created by Murray Bishoff of comic shops in 1979. The list is definitely not complete because it doesn't have the shop I was going to in the Bergen Mall in Paramus, NJ at the time, but it does show a lot of shops around Washington, although none in the city itself.
Here are some clips showing the local shops, only one of which still exists, I think. The Maryland list shows Barbarian Book Shop, now Barbarian Comics, which is still roughly at the same location. UPDATE: It's beyond our coverage area, but Randy commented that Zeno's Books is still in business too, and on their Facebook page, they say "40 years of serving Tidewater Virginia’s oldest Comic Book Store."