For stamps that I use at reenactments, I prefer to find old German wooden stamp handles, strip off the old rubber and re-use the handle. I search for “Holzstempel alt” or “Holzstempel Konvolut” on eBay. de.

Wood stamp handles in the old style are still made and available in Europe. Jackson Marking Products is a US source for handles in the proper style.

For stamps that I only use at home, I cut simple wooden blocks. I used to use a cheap back saw and plastic miter box from the hardware store. Now I use a band saw. I just cut up scrap wood.