Where to find a heater control valve

I understand the water valve is not proportioned, but rather open for heat and closed in AC mode. In heat mode, your heater slide knob opens a door that lets in cooler outside air. Not sure how they controlled cooling in 1965 (climate door, AC cycling, ... several methods).

My 1964 & 65 are not factory AC, so no under-hood "hot water valve". I hope to add one just to insure no flow thru the heater core in the summer, though not essential since I will use a separate "knee knocker" AC box w/ its own blower. I bought a few plastic heater valves for newer Fords ($7 ebay). You could do similar if not concerned w/ "factory correct". They have a single vacuum line w/ spring return. I need to use a vacuum solenoid for control, actuated by a 12 V signal that is on when the AC box is active.