A well stocked artist's supply store will carry small razor blades that fit into a compass; a compass being, for those that may have forgotten, a draftsman's tool for making circles. As I was a graphic designer by initial education I have a fine set of Kern (Swiss) compasses, and the small razors that substitute for the normal [pencil] lead that goes into the compass. Today, there are also a number of low cost circle cutters available.
Using these two items, I cut new gaskets and punched (with a small hold punch) holes in them for the screws, and they were flawless reproductions.
Of course you can cut the stuff with a scissors, and punch holes with pointy things, and it will work. I did not use any gasket sealant.
