I broke the bottom of my blend off that connects to the metal adapter. Where could I buy just the blend door? Anyone have a used one?

 

I am having trouble getting cold air. I have removed the actuator and manually moved the valve by hand and can get all the hot air I want but when i move it to cold it dont get all the way cold.

Is there supposed to be hot water going through the heater core at all times? Can I install a couple of valves under the hood at the firewall on the heater hoses or will it prevent circulation to something else?