For some reason, Thetford is weird about selling the gasket kit alone. You may have to buy the entire Slide-EZ valve, part number 12836. I've done it both ways, but it wasn't easy. As you may have read, I had to threaten them with a $400 warranty repair if they didn't send me $2 worth of gaskets. They sent the gaskets.
In post #14 of the thread
http://www.trailmanorowners.com/foru...ead.php?t=5890
Dave / ShrimpBurrito gave links to a couple suppliers that still seem to have the gasket kit. Have you checked them?
The Slide-EZ valve is still advertised as being in stock at RV parts houses like PPLMotorHomes. A little pricey, for sure. Beyond that, when you ask about it, you might do well to describe the toilet as the Electra-Magic toilet, rather than RV-80. But I have found no indication that the toilet itself has been discontinued.
Bill