I'm not sure how the one in the AD trucks is made, but I made my own filters for both the high beam and turns signals with items from the local hobby store. For the turn signals, which is basically a tube with a frosted plastic filter, I used a peice of sheet plastic (.010") cut to size, the epoxied to the original tubes. The plastic was them painted with Tamiya Clear Blue paint, recoated as necessary to get the right shade (I know, they're supposed to be green, I wanted a kustom look). For the high beam, which was essentially a plastic rod that's necked down to be retained in the housing and rounded on the ends to act as lens, I replicated it with a peice of blue acrylic rod, aluminum tube, and a cabochon decorative bead. The rod was cut to length, with the tube epoxied to it in the same position as the original peice, then the cabochon as epoxied to the end, once the "mirror" backing was removed. The acrylic rod is used primarily as a light pipe, so it worked perfectly for making the lens, though I did have to add a bit of clear blue paint to the ends to darken the color a bit.
Side note, on the turn signals, I used painted clear sheet plastic. For a closer to original look, .010 or .005 white sheet could be used, as it is thin enough to let light through, but will give the fronsted look. It would still require painting with a clear paint. Another option would be to use colored acetate sheet, also redily available at the hobby shops in several colors.
