You have just defined the problem. IT IS A SMALL MARKET. The expenses in importing a few cases of BP shotgun shells does not justify the return that a Dealer would make on them.
As ANTIQUEGUY has pointed out, it is simple enough to load your own BP shotshells. You can still find paper hulls, especially at gun shows or some of the importers who bring in Russian, Polish or other European shotshells. Plastic hulls can be used if necessary. Fibre Base wads and Filler wads are available, and even some of the slightly larger in diameter wads for loading BP muzzle loaders. LEE still makes a 12 Guage LEE LOADER for about $35. Even better, you can buy Brass 12 guage shotgun cases for loading BP shotshells and these will last a long time if you do not crimp the mouth of the case in slightly. A top wad can be punched out of old cereal boxes, and a few drops of glue will hold it in place.
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