It's strange how the late 40s- early 50s glasses seemed to flake in the non-lit areas. Where as the 60s-70s seemed to flake in the lit areas.

Pretty rare game. The chances of finding something in nice shape sitting on a shelf somewhere is not impossible but seems unlikely. I'd love a perfect upgrade for the marginal backglass in my 1950 Skee Alley. About as good a chance and in the 10-15 years I've owned it have never seen a loose glass available.

BGResto or something along those lines will be your best option. Tricky part is there is enough missing art and so few examples you may have to take some liberties redrawing it.