We restored a 1909 International High Boy that had sun faded tail light lens we named "Unicorns". Some serious cleaning and sanding with 2000 grit was followed by spraying with Vinyl dye which is more translucent than paint and looks correct. Don't know if this helps but I would try it on a small area first. You can also make a lost wax mold and cast new ones with clear resin tinted to the right color.
