Thanks for the suggestions.
The valve appears to close but does not completely seal. I spoke with Joseph and his plumber yesterday and they don't have any source.
I checked on having one shipped here and in order to have a chance of getting it here before I have to leave would cost $75+.
As long as I am hooked up at the park or have the cap in place it is not a "biohazard" issue. If I dump and flush before I disconnect and don't use the toilet while disconnected then I will survive. As long as I dump the black and add significant water every other day to keep the smell under control I can wait till we get back NOB.
However... If anyone is on their way to San Carlos or Guaymas, and may be stopping at a Camping World on the way, I can have one paid for and waiting for pickup. Dinner on me if you could carry the parts down.
Thanks
Steve