You might try 16 ga.com and shotgun world. I bought 100 new Activ hulls in 16 ga a couple months ago on shotgun world. That’s all the guy had, but there’s probably others out there.
BTW some “a hole” tried to scam me. He answered my wtb ad. I asked for a pic of the hulls and he sent a pic that he found somewhere and the hulls were not Activ. And he only accepted e payment.
