Frank is spot-on: you'll typically want to size up 1 to 2 inches from the size that you take in trousers. At least for the Carmina and Epaulet-branded belts that we sell. It should put you comfortably in the middle of the belt.
Python would have to come from Carmina, especially if it's exactly matched to their skins.
Gator and lizard though, I can easily make here in the states. In pretty much every normal color. I don't imagine that I would stock those items, but drop me a PM if you're interested - we can certainly do a special order for you.
Gator belts would be about $375. Lizard about $115. And Crocodile about $225. The exact price would depend on the width and size. Turnaround is pretty quick - about three weeks or so. And it would include both silvertone and gold tone buckles.