Panzerschreck glass

[openwire]

I've been seeing a LOT of supposed old stock/barn find/whatever Panzerschreck glass for the blast shield for sale online.

Since my Panzerschreck arrives Monday, I've been shopping accessories and spares, and I'm struggling with the notion that so much of this glass supposedly exists still. Are there any educated thoughts on what's being sold on eBay and elsewhere? I'll have three original pieces so don't really need more, but hey, spares and accessories are fun.