Jason does sell his blanks, if you want them the easy way.
If you want to make them, you need a saw that is very accurate and will not "slip" once the setting is made.
There are 360 degrees in a circle, so if you wanted 4 pieces, you would cut them all 90 degrees. 12 segments, 30 degrees.
Do this enough times and then check your fit.
I saw him assemble one at an IAP meeting--made it look easy--personally, I would buy them---but you sure COULD make them---
Hope this helps
BTW, Jason does a week long class on how to do it, so expect a few failures.