Go to any auto parts store, ask for exhaust gasket material, about 1/8" thick and make your own. It will be better quality than any replacement gasket.
The metal, copper or aluminum gaskets are good but they rely on a flush mating surface. They will not conform/seal to warped or uneven gasket areas. Almost without exception the exhaust flange is warped from it being welded to the pipe. It needs to be dressed flat before you can expect a gasket of any kind, to work well.
Tom