make your own.
if you have access to a wood lathe, or even a metal lathe and some thick plexiglass that's weather resistant, you could copy the shape of the original lenses. it'd require serious thick acrylic or other correct plastic, but it could be done easily. after turning you could drill the two mounting holes on the centers of the original lens. this would be an easy way for me to turn a couple of rear lenses out of red so i can put in a twin element bulb. the low element for park/tail, and the high element for turn. that would take some study to figure out which type of plexiglass type of material would be good to use. perhaps lexan. ideas?