I was poking around on the internet and it seems that Fontana is used in rv's and boats and the common opinion is they are trouble prone.
I didn't see any dedicated parts source for them but based on the threads I read they use common Moen cartridges .
Most people that posted were removing them all together and replacing them with other faucet assemblies.
Shut your water pump off or remove your city water supply and pull that cartridge out . It's broken now so you really don't have much to lose.