I imagine mouse-pads are printed by some sort of screen
printing process or a vinal print-cutter. But as for creating
your own, I imagine it could be quite costly to set-up.
Anyway here's a few links for you to check-out.
All these companies produce custom mouspads.

http://imageworks.0catch.com/Index.html

http://********inprint.com/mouse.html

http://www.exclamation-mouse-pads-cu...ouse-pads.com/

http://shopping.oraclesmallbusiness....ias=/mousepads

Hope this helps.