Black, you can use a lot of things to make hotwire templates. I use cardboard/art board for my templates. its about 1/16" thick but has a good regidity to it. If I have a really thin section of a template I use some super glue to stiffen up the edge to keep it from bending on me. I use my cardboard templates over and over with no issues.
If there is a cabimemtry shop in your area you may go and see if you can get some scraps of formica. Since table tops are expected to have thigns like, hot plates or pots on them, they use a high temp formica to cover the tops of tables.
Most any wood will work as a good template material. Wood has to be several hundred degrees to ignite. Foam needs around 140°-160° to cut with a hot wire. the most a hot wire should do to wood is darken it if you leave the wire in one spot for too long.
As for sites with templates, templates for what? RCGroups has a scratchbuilt foamies section with lots of plans for all types of planes. You can take almost any plan for any plane and use it to make a hotwire template. I've been doing hotwire cutting for 5-6 years now, have built multiple power supplies and cutting rigs. Im not saying I am an expert, but I do have some info about the process if you ahve questions, along with many others.