Replacement thermostat mixing valves
Are very hard to find for these machines, they're fairly standard, Dole inlet valves in most cases.
Normally, when I have to deal with one of these, I replaced the valve diaphragms that makes them work fine again if there are leaks from the metal plate, where the five screws hold the thermostatic element in place you can just carefully remove it clean the seal and coat it with 3M marine sealant and put it back together that should solve the leak.
Usually, this is sufficient to make these valves work great again, unless you have a valve that had frozen repeatedly or otherwise cracked body. You should be able to save this valve.
John