A piece of rubber gasket material from Ebay and a pair of scissors would probably be a simpler option than trying to find something from nearly 60 years ago. That material is available in all sorts of sizes and thicknesses at dirt cheap prices. Use the old one as a template to whittle out a new piece.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!