There aren't a huge number of members here with machines with glass panels likely to need replacement, most that do have either ex-educational, home built or new equipment, it's not a particularly fertile hunting ground for sales of aftermarket transparent panels, add to that the level of all around DIY experience and I'll bet that most, like me would source and fit suitable replacement materials locally.
If a panel gets broken on my new machine I'll replace it with laminated glass and apply a transparent film to the outside.