After a lot of searching ...my buddy and I found 1970 MOPAR Plymouth B Body (Duster) side marker lenses that are almost the same size as First Gen Vega. They come in amber and red and are reproduced. See Pictures below. We slightly beveled the edges of the Mopar plastic backing to fit the recess and then drilled two holes in the lens matching stock lens hole location. You will also need old worn out Vega lenses as you need the back piece white plastic which is the bulb holder which then mounts behind the fender. Finally locate a couple of screws slightly larger than the stock ones and simply screw together as a unit. Sounds complicated but actually pretty easy.
Note~The Duster lens is not as orange as it appears in the pic.