I've made and sold
12 pairs of the taillight adapters this summer........on hold for now, while we scramble to get our retirement cottage finished; but I'll probably start making them again in late September.
Price varies, depending on what the client wants me to do, but starts at $110 per pair, in primer. More, if you want them painted in something like the U-Haul "cream" color... and if you want large openings for the inset tail-lamps.
You can PM me for more details, or email me at firstname.lastname@example.org
You may wish to consider 2 other options, as well.
 Several people on the U-Haul Facebook site are now selling their cast-aluminum taillight adapters. These are a genuine U-Haul product, though not made for the campers, so they don't match the corner curvature precisely..... they do offer the potential of being sanded and polished up nicely, though.
 Another member on the U-Haul Facebook site is hoping to have new taillight lenses in production soon. No prices yet, and not ready to take orders yet..... but that possibility is out there.
Those are the 2 options to my F/G adapters, at any rate.
p.s. the black you see in the one picture isn't a gasket, but remnants of the old U-Haul rubber pocket that held the bulbs behind the original lenses. My adapters fit snug enough that the gasket material I purchased turns out to be too thick....... most folks are using a little rope of butyl caulk to seal them to the camper body.