No clue to the answer to your question but it’s not difficult to load your own ammunition. Gun powder, shells and slugs aren’t usually as heavily regulated in the US I’d assume to some degree that’d be true elsewhere. Can prolly buy it off eBay or craigslist if you really looked.

Then it’s just a matter of measuring and packing it all into a single bullet with a special fitted hand press. Super tedious and time consuming but easy to do. Wanna say old timers did it back when it was cheaper but the only people I know who still do it do it to controll their ammo consistency for either competition shooting or rifle hunting.