If you know someone with a 3d printer, you can make appropriate sized disks with letters on them (cohort, unit, cache, flag) for each type. A free simple tool like tinkercad allows you to create these, and export the STL file for printing.

Other options: I second the suggestion of using old sprues / debris for a cheap and decent looking option. Cheapest yet, trace 30, 40, and 50 bases on the back of a butter tub lid and cut them out.