75 impala a/c control thumbwheel

I'm looking to find out if anyone knows of any supplier that would be able to supply the heater/a/c thumbwheel control.It would also fit 71-76 Chevy B-body with C61 a/c.GM can no longer supply this part.If not the thumbwheel,a complete a/c control unit would do.Your help would be greatly appreciated to fix my a/c.My old girl needs some TLC.
chuck's