You can make a gasket out of a can or any sheet metal, like aluminum, copper or brass. At a thickness of about 0.10mm it is very easy to cut and trim with a pair of scissors, there is nothing to it. Size is not that critical as long as the surface is smooth and the material soft enough go give a good seal. I think you would be better of to use a fuel that you can easily get (more consistent fuel in the long run) and just trim the compression to suit.