I did find some "rubber" gaskets yesterday at Tractor Supply. I bought several packs.
As a side note, my mail fresh water hose that I have used full time for the past 4 1/2 years started leaking when I was setting back up after a move. I was leaking right at the pressure reducer connection and it was not the gasket. This original brass (thin) fitting finally started leaking through the fitting. I will probably just retire this hose vs new ends, etc. It was the first hose I bought when I started full time and I don't remember the brand, but it was originally 1/2" and now it is probably closer to 3/4" due to swelling. I have been watching it for months to see just when it would blow. If it wasn't so stiff and impossible to roll up I might repair it just out of nostalgia. But I think it is retirement time.
2006 GMC 2500HD CCSB 4x4 Duramax/Allison, Titan 52 gallon fuel tank, Prodigy Controller, B&W Companion Hitch
2010 Jayco Designer 35RLTS, Cummins/Onan RV QG 5500 EVAP, Progressive Industries EMS-PT50C, TST Systems 507 TPMS, RV Flex Armor Roof