Exactly. H&N and JSB might be a little slow in making them with other calibers being more popular, but they're not going to stop knowing there's still a quite large market for them.
I made it a habit back 5 years or so ago when I got the first of the now 9 rifles I have in .20 to either outright order pellets or add a couple tins to every pellet order (I also have guns in 3 other calibers) and have a pretty healthy stash. I'm also one of those Sheridan shooters you mentioned

Someone wants one, I always say go for it, buy and try one. End up deciding you're not a fan, there's always someone out there that will buy it from you.