That part number is probably a component part of the mirror assembly. It would not appear in the MPC (aka Ford Car Parts) because it is not serviced. You will not replace it, you will get the whole mirror assembly. With the "Z" in the third position (C9ZA-), it was designed for Mustang use.
Jim
PS: The majority of part numbers in the Ford MPC are "service" related. There are a few "engineering" part numbers listed, plus a few Mercury, truck and other product lines included. The actual part in the box often has the original design part number. It's "service", not "concourse" related.