Those gaskets are intended to keep the drums from rusting tight to the hubs, and it looks like they did their job well. You can make new ones from something like a file folder or some other piece of thin cardboard if you can't find a source for the original gaskets. Use a brake drum as a template to locate the holes in the right place.
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!