The PageFlip seems like it would be ideal for what you want to do. It's designed for flipping pages with scores and such, but there's a free that allows programming the switches to do basically anything a QWERTY keyboard can do. It's really pretty clever...I've reviewed the three products PageFlip makes in the Reviews
section of the library at craiganderton.org
...check it out.
For heavy-duty applications, there's also X-Tempo's Pok
, which has 8 footswitches.
I own both, and they're both sturdy enough to handle foot stomping