I would look at Eletro-Voice and Yorkville to start with. Both have some pretty good options to choose from.
These from EV might be a good place to start:
http://www.proacousticsusa.com/productd ... ?pId=11110
All this said, I personally don't like the idea of in-wall speakers for a live audio application. Your best audio still comes from speakers held in an enclosure that was designed for them and for the best possible audio response. Sticking them inside a wall certainly doesn't have the same characteristics.