You can buy kydex a moldeable plastic on Amazon.
https://www.amazon.com/gp/product/B004U6VBU8/ref=ppx_yo_dt_b_asin_title_o02_s00?ie=UTF8&psc=1
https://www.amazon.com/Small-Parts-KYDEX-V-Sheet/dp/B004U6VBU8?th=1
for me, I just used a sharp utility knife and bending and it would break along the scored line.