Hi.
There is a solution to your cap problem.
Get some hold on empty 7MM caps and refill them.
Shipping empty caps should pose no problem.
Refilling can be done by creating a superfine Armstrong's mix , with a minimal amount of binder (<5%) and put it as an emulsified putty inside the cap. You can add some dark German aluminum or magnalium for some extra flash.
It is tedious and a bit tricky to get the right amount in, to avoid cycling problems, but do-able.
Also if making Armstrong's mix is no option, you can buy firing cap reload kits for preppers. They use it for re-using the firing caps of spent shells. It's a two or three component mix. This powder will do fine too. Quite sensitive to shock and powerfull. Same method of getting the emulsified mixture inside the 7mm plastic caps.
Once a method is found to make 7MMS caps or something that can replace them, it would be quite a Rosetta stone in model gun land. It saves stocking up on caps and being overly sealous in the reluctance to actually use them.
Hope this helps.