All the Ford Model 'A's did not
have a grille. They had a radiator shell that left the finned area of the radiator exposed.
There are aftermarket 'shields' (rock guards) that cover the front of the radiator and the radiator shell. This may be what you are looking for.
Check Mac's Antique Auto
, and/or Snyders
. They all carry the piece you need.
Below is a photo and the part # from Mac's Antique Auto for the 1931 Model 'A'. Left click for a larger view.
The part # is A18700C