When I made the plugs for my RMC type B I also made the washers, Just drill a 1/4" hole in some thin copper sheet, mount on a mandrel and then turn the outside round. Or just turn down one sold for steam fittings.
I think non stick oven liner sheets are a source for the gasket material, at least that is what old John Bogs used to suggest. Plenty on e-bay. Mylar is another sheet that can be use dfor gaskets.
Edited By JasonB on 14/08/2020 07:02:17