I wonder which years of MoPar rear window defrosters are the same units as 1957. As far as I have seen they look pretty much alike from the 50s to the late 60s.
I have the dash switch, the vent bezel for outlet and the inlet "speaker grille" bezel from 1957 so I would need just the 6x9 blower motor setup, the hose and the duct to complete the defroster.