"Inside-out" seal

[motto]

That seal is rather unique. Especially when you consider that it doesn't only have to keep lubricant in but also keep water out. It looks as though Richard has come up with a source for a replacement. I no longer have a DUKW SNL but the GM number given (2199398) looks good.
I have installed conventional seals in that position but have not immersed them so can't comment on their effectiveness for amphibious use. You could install them with the lip outwards to prevent water entry and pump grease through after service. Assembly using conventional seals is a little tricky as the seal must be on before the bearing cone and tapped into the spring mount as it is installed.
I have any amount of NOS pressed steel adaptor rings that are driven into the spring seat but no spare OEM seals.
When I purchased the surplus dealers stock many years ago included with it was 3,000 of the early type felt ring you mentioned that were obsolete during the war. I didn't know what to do with them and at the suggestion of a friend donated several hundred to a local kindergarten for the kids to play with. I still have a few about the place.

David