Luverne Drop-Center bumper license plate light lens

I have a 1994 F-150 equipped with a Luverne 9408 8-inch drop-center bumper. After 23 Minnesota winters, the license plate lenses on the bumper have all but disintegrated. As such, there was nothing to diffuse the light from the bulbs, and the plate wasn't being illuminated hardly at all. After being given a verbal warning by a police officer who thought I didn't have lights on the plate at all, and discovering that Luverne doesn't make anything like this anymore, I decided just to make my own ba