Do you need just the plexiglass, or the hardware too?
I know Memphis sells replacement plastic and I'll bet National Cycle does as well.
I really only need the polycarbonate. I installed a windshield bag earlier this year that had tabs that fit under the cross support of the windshield. Apparently I over tightened the bolts resulting in spider web cracks on 3 of the bolts. The problem I have is identifying what model it is as I cant find it online.
I did call National Cycle & the CS rep said it was probably what they previously sold as "one piece heavy duty" but it's no longer in production or available. So no luck with that option.