Reddit reviews Jack Richeson Medium Density Untempered Hardboard(12 pack) , 6x6

Thanks now I can Reddit good.

What you could do Is use mdf (that stuff clip boards are made of) and drill holes into it. You could even use a 2d printer to print a template out. Mdf is a lot easier to work with than plexiglass.

You can find some here

3mm mdf on amazon returns with several options.

Try this, you could inquire before purchasing:
https://www.amazon.com/gp/product/B01E5YICCE/ref=s9_dcacsd_dcoop_bw_c_x_1_w

Also maybe this:

https://www.dickblick.com/products/hardboard-panels/?clickTracking=true&wmcp=pla&wmcid=items&wmckw=14945-1008&gclid=Cj0KCQiAiKrUBRD6ARIsADS2OLmrH6TiTQ2PSY-sETOF4Bl5L-tRVPe73QDpC4EN90b7YRykAcjuUOMaAi7oEALw_wcB

I've a friend who does laser cutting and he gets his at:
http://www.artistcraftsman.com/

Good luck!