Back when the .500 first came out, I tried to interest CCI in making shotshells for the .500 Mag. They said too little probable market to justify the tooling costs.
Yes, I know some have produced homemade shotshells that work OK, I have as well but I don't think anyone can readily duplicate the shot capsule CCI uses.
I tried again, same answer but was told I was hardly the only one asking.
Maybe we can try the "pile on" tactic. I called 800-627-3640 and asked for someone who deals with CCI pistol shotshells.
If interested, you might try but perhaps space your calls out so they won't suspect a setup. I think there are enough .500 Mag shooters out there to buy a good number of these if for no other reason than just to have fun. Don