Help with outside door trim - Newbie

I just got a 1990 Lumina Euro. I do not know much about the car, but it seems to be a good car. It does ride rough in the back, but anyway......the outside door trim piece on the drivers door behind the window is broken. This lets the window stay open a crack at all times. Does anyone know what this piece is called, and where to purchase another one? Thanks for any info!!

Probably a salvage yard would be your best bet.