Have you had no positive response to contacting customer service and asking them to carry a product again? It's quick to do and sometimes works, also for getting them to carry things they don't already when they already get stuff from that same manufacturer. IMLE it's the particular store's customer service you need as they have some local power over purchasing decisions.

No, I haven't. I've tried it twice; on one occasion they said "we'll see what we can do" and nothing happened, and on the other occasion they looked very confused at me, ran back and forth like headless chickens, summoned a supervisor who said nothing readily comprehensible, and eventually said there was nothing they could do.

After that I wasn't sure I had the energy to try again :-/