Heater control valve

"It used to be" that real parts guys working at real parts stores had numerical/ interchange/ pictorial guides. Various manufacturers, you could look thorugh the book and find something that works. I'd try to find some "old" guy that's been at a NAPA a long time and see if you can get him in gear. You don't need an exact fit, there is lots of room. But you will have to determine if vacuum opens it or closes it.