MD you can pick them up at any walmart in the craft/fabric section. the roller comes with a rubberized board. Its no problem cutting through 4 layers of material. Even as thick as that. I cut flannel 4-5 layers thick in one pass. This is the one I got:
http://www.walmart.com/ip/Fiskars-Ro...g-Set/12335930

Just be careful because those buggers are sharp!