I met a lot of great people playing Waka kickball and DC kickball too. You can join random teams, and meet new people. It take a lot of energy to meet new people but it can be done! Trivia nights, local organization events, and the like are also great spots to meet people. It will take a little time and some effort you might not be used to spending to make friends, but we’ve found it pretty easy.
DC is a great place to meet new people because there are a lot of people in the same boat you’re in. It may seem intimidating, but a little conversation will show you many have been where you are and are willing to include you.
2 years here and we have a wonderful circle of friends that I would have never had anywhere else. Be open, make the effort, and try new things! Good luck and welcome to DC!