If you have the left overs and can measure the thickness, go to the auto parts store and see what they have in gasket material in a similar thickness in a black, high temp material. Easy enough to make with a sharp Xacto knife and some circle templates. Cut the center hole first and get it to fit properly and then use a sharp o-ring pick or ice pick to mark the hole locations Sharpen up the end of a length of 3/32* tubing to use as a punch to cut clean holes. Then cut the outer diameter. If you can find some of that green gasket material that Perfect that will work if it's big enough. I think an old playing card will work also. That material is pretty tough and has a nice coating on it that helps with the seal. I've used bad original ones in an emergency that had a thin coating of #2 Permatex on both sides and the engine ran well with no leaks. I don't think soda can stock will be soft enough and thick enough for a McCoy .35, but I have never tried that.
Type at you later,
Dan McEntee