Hire a lawyer, folks. Don’t bother chasing after Etsy support cases when this happens. 2.5 months for a reply means that a lawyer was almost certainly not involved, that arbitration was not invoked, that Etsy’s actual human lawyers were not engaged, etc.

"In the meantime, you can still buy blank cartridges and GB Interceptors from FerranteCraft's Etsy store, but everything else will have to be bought from the publisher's website." [emphasis mine]

This is really the solution here, thankfully they already have it up and running. Unfortunately, I'd bet it gets very little traffic compared to Etsy. This whole centralization of everything on the Internet thing onto a few large sites that really don't care about their users has been deeply saddening to watch.