Also interested in the answer to this question.

If it’s still in some what decent condition. You might be able to find a local shop to match and cut a new piece.

how is it secured? that looks like something that could be easily replicated in PETG and laser cut

I don't think I've ever seen a replacement for sale. The window is held in place by 10 nylon screws, I believe they are 10-32. It's 3.1mm thick and has squares routed out about half the thickness of the plastic to give the epoxy something to grab on to and hold the screws. I have some SVG's for the window with screw locations and the black vinyl sticker that goes on the top. The overall size looks good but I did measurements for the screw locations when the window was out to clean and I don't want to remove and re-level it to check so they should be double checked. If you have a laser cutting place near you it shouldn't cost much to have them cut a window.

https://drive.google.com/open?id=1-eA7IHuMMVwcdUGLymmsPqwTM3tXPNag

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