When you say "primers", I assume you mean the priming modules. For the actual primer, they use any LR or LRM primer.
They are very easy to make. You can use 308 cases cut down to about 1.07" or less. Length does not matter, unless it's so long the case mouth hits. This design headspaces on the case head thickness between the base of the cartridge and the inside of the case at the flash hole. That's the only distance that matters. You can also use any case with a 308-size head (30-06, 270, etc). You can also use 45 ACP cases with no cutting involved. I've made many of these.
I've also done some work in blueprinting these cases for a perfect headspace fit, for better seal and accuracy, by picking the ones that the bolt has just a bit of resistance on closing, then measuring that distance, then sorting cases for that distance. Of course, because of how the headspacing works in these, you want to do all your primer pocket and flash hole uniforming BEFORE doing any measuring.