If you're adventurous you may give it a whirl yourself - I've bought Lucite and Plexiglass from sign shops before for a couple different applications - You can get it in about any thickness and it's fairly easy to cut - I used a Black & Decker handheld jig/scroll saw and smoothed the edges with succeedingly finer grades of sandpaper - The nice thing about Plexiglass like that is that it usually comes with a protective paper sheet stuck to it to prevent the plastic from getting dinged during cutting and shaping - when all the works done you peel off the protective sheet.
It drill nicely too -
I'm not familiar with how the panels are attached to the frame portion of the side curtain, but it's probably not that difficult to repair - gotta be screws, rivets, adhesive, etc.
Give er' a go mate!