Head gaskets made from aluminum turkey pans the type that are about $2.00 or so at Walmart or the dollar store. cut it out with scissors. Coat both sides of the gasket with cheap aluminum spray paint then install it.
Auto parts stores carry gasket material, most gaskets on these engines will use 0.025 to 0.030 thickness material. If you live close to a industrial engine shops or industrial gasket shops they will give you their scraps. You might even find the aluminum gasket scraps there too.
I show how to make your own gaskets on some of my stickies if you will look.
cereal boxes work as does some poster boards for gaskets, it ain't rocket science to make a gasket.