You can try 4 layers of tin foil together, press it on to the pieces you want to duplicate to make a mold.
Then take Fiberglass and Resin and put it into your supported mold to make your new replacement grille parts.
Trim to fit and glue them in carefully with some more fiberglass and resin. Final shape, then paint to match.
I have taken wax paper and spray adhesive, the spray adhesive holds the wax paper in place then you cast your new part off of that. Nice part about the wax paper it will release the fiberglass once it has hardened.
Creative Fixing . . .