Which one?

The small avionics cooling air scoops (p/n 1470219-1) are over $639 new from Ce$$na!!!! (I know, right?)

http://www.cessnadirect.com/1470219-1.html

The fresh air door on the passenger side (p/n 0453002-7) is apparently unavailable new.

Either one, your best value will be at an aircraft salvage yard.