Washington DC is where some of the biggest decisions are made. Obviously yerba mate has to be present for those big decisions. Below are a few of the cafes we found that sell yerba mate.
La Union Grocery has been in business for over 28 years and they have a ton of Latin American cuisine options including yerba mate. They even have Salvadorean takeout options.
Tango Pastry has awesome reviews and awesome Argentine food including milanesas, alfajores, and medialunas. Made my Argentine chefs, you can't get anything closer to authentic.