I've also seen them at a local organic-y place near Davis Square.

In addition, whether or not they're "meal kits," you see more and more "one bowl meals" and the like (that you can add meat to if you're so inclined) in the produce section of grocery stores.

Mariano's in Chicagoland also sell meal kits now, as do the Amazon Go stores, one of which is conveniently next to a major train station.