I stopped by Colorado Plastic Products in Boulder today. They sell scraps of all sorts of materials, including high density polyethylene (HDPE), polytetrafluoroethylene (PTFE/Teflon), and ultra-high molecular weight polyethylene (UHMWPE), all of which are attractive for making ice carving tools.
I needed a low friction surface for a new hot wire ice cutter I'm working on, so I picked out a nice sheet of UHMWPE. It has terrific properties for the application, including a low coefficient of friction, low water absorption, and a wide operating temperature range. Lars had suggested the stuff because it is used for ski bases and dog sled runners, so it should work very well.