Air Vent flapper?

[56sedandelivery]

So tearing down the inner fenders and find that the flapper that controls the ventilation in car and the heater blower has gone south. The gasket around the flapper that seal the vent so that you do not get outside air when you do not want it is shot. Has anyone replaced this or fixed somehow. I know the parts book show only the entire unit. I assume these are no longer available and any old one would probably be in the same condition as mine. What have you guys done to solve this?