Does anyone know if I can get a cap for a 61 at like Camping World?
If your coach hasn't had its plumbing updated, you will likely find that modern termination caps will not fit your coach's plumbing. There have been at least two owners of Vintage (early 1960s) coaches who have undertaken extensive searches to find the aluminum "pancake" style termination caps.
Take a look at your plumbing where the terminator fits, if it has been updated it will likely either be white or black plastic. If it is white plastic a Thetford terminator cap will likely fit; if the fitting is black plastic then Valterra will likely fit. Valterra fittings will likely be available at nearly any camping supply outlet, while the Thetford may be special order catalog items at some of the
"volume" camping supply places.
Good luck with your coach!