Have you tried Gemini yet? https://www.cryptocompare.com/exchanges/gemini/overview You will see they are saying it is specifically mentioning Washington DC as one of the states that are supported. ^smile^

For more information, read more here : https://en.wikipedia.org/wiki/Gemini_(digital_currency_exchange)

Hope this was of any use, some people have moved away from Coinbase to Gemini, due to Coinbase's poor support and attitude towards it users and lately some capacity issues.