Don't recall the name, but there is a tea shop upstairs between Berkeley and Clarendon. It's over the little basement Italian cafe. They have the tea loose in jars, so would think you could create your own blends.
The coffee shop is L'Aroma Cafe and the tea store is on the second level of the building and is visible from the street if you look up. I don't know what it's called but it's not Whittard's of Chelsea, which is on the opposite side of the street a block or two closer to Mass. Ave.