Being in Arlington/CC that puts you pretty close to all the DC teams as well as the Arlington squads. District Velocity, Squadra Coppi, NCVC, Artemis are all teams that are very active in the area.
First I would sign up to the MABRA listserv, most teams announce their sponsored rides and races there. Then I would just start to show up to the popular DC group rides and talk to people on the various teams.
Freshbikes Tuesday ride (April-October) is one of the biggest, once a month they have free Baja Fresh tacos and beer.
Saturday mornings at East/West Highway and Beach Drive is another huge ride. They have a 7am and 10am group.
Thursdays at Hains Point for sprint practice. well really everyday at noon there is a group that does loops at Hains, but on Thursdays there is a big group in the evenings too.
By the way, i are you the same echappist from ST?