"up the creek"
those things are not visable from the outside of the car. If I needed a replacement, does not look to difficult to fasion a suitable replacement from piece of red tinted thin plexiglass. Either one strip, wrapped to make a circle, perhaps formed a bit with heat from a blow dryer, or a couple of pieces super glued together.
There are pegs on one end that fit into slots-holes in the taillight housing, the end closest to the lens is held in place by friction in a piece of foam. Don't see much critical...
