I bought a M3i Zero from RHS.. It works great so far. (I was a little hesitant about ordering one because of how many people have bricked theirs.)
Very reliable, Fast shipping and Excellent customer service
The only game case that can hold more than 10 games (That I'm aware of) Is the Nintendo DS Game Card Case 16 just search for it.
It's pretty compact so it shouldn't slow you down. (Though I don't believe it's "pocketable")