I get mine at www.millerslab.com But you have to be a pro to sign up with them. They also own MPix.com though and you don't have to be a pro to get prints done there. Maybe they do the die-cut with their wallets. A lot of people here use Mpix, so maybe someone will know.
I am professional and I use MPix, I'm thinking of going with Millers sometime. MPix die cuts with curved edges and I really like their prints.