Derek I have some 00M00 30 casting silicone (made by Smooth-On) for making a new Arig mold. I haven't used it yet but my grand son used it to cast an adapter so his tazer would attach to his glock. It worked great. Checking the specs it is only good to 500°F. However, they make lots of stuff and may have something that will work for you.
They have a toll free number and advertise that you can call anytime with questions. 1-800-762-0744
If you want to make some cheap practice molds before you plunge into costly material, shoot me a pm.