There are several brunch spots in Boston that offer bottomless mimosas. Here are a few popular options:

1. The Beehive: Located in the South End, The Beehive is known for its lively atmosphere and delicious brunch menu. They offer bottomless mimosas for $20 during their weekend brunch hours. You can find more information on their official website.
2. The Friendly Toast: With locations in Back Bay and Cambridge, The Friendly Toast is a quirky diner-style restaurant that serves all-day breakfast and brunch. They have bottomless mimosas for $15, and you can check out their menu and locations on their website.
3. Liquid Art House: Situated in the Back Bay neighborhood, Liquid Art House is a unique combination of a contemporary art gallery and a restaurant. They offer a brunch buffet with bottomless mimosas for $25. You can find more details on their official website.

These are just a few examples, and there are many more brunch spots in Boston that offer bottomless mimosas. It's always a good idea to call ahead or check their websites for the most up-to-date information on pricing and availability.