I'm sure others will chime in, but if you have a car, College Park Bikes and Mount Airy Bikes (
https://www.bike123.com) are worth a visit. Mt. Airy Bikes is like a museum, and College Park Bikes, while smaller, has quite a variety. Conte's Bikes in Old Town is just a great, friendly shop, and although not a Riv dealer, they carry All City. Big Wheel Bikes in Old Town, close to the river, is a small shop, with new and some used bikes for sale. Last time I was there, they had some old classic bikes (Colnago, etc.) for sale. Wheel Nuts Bike Shop, on the north side of Old Town, is a friendly shop. Velocity Co-op is in Del Ray, if you're looking for use bikes.
Enjoy your stay,
Tom