Given my track record for predictions, you ought to take this with a ginormous grain of salt.
If you look at the evolution of military firearms, going from bolt action to semi-auto to full-auto, I think that we've run through the range of what's available. Oh, stuff will turn up - look at the Chinese M44s that just popped up. And there's the continual stream of Mosin-Nagants, although they'll end someday. But I other than the M-Ns, I think that the bolt action stream is drying up. The semi-auto stream is a bit more difficult, given the requirements of US law and just what was actually made.
Maybe there will be some handguns that pop up. Given the moving 50 year window, perhaps at some point there will be a surge of milsurp pistols available.
Anyway, like I said, my track record for predictions of any kind is terrible. In fact, you could bet exactly the opposite of the above and probably have a much better chance of being right.
Well we don't rent pigs and I figure it's better to say it right out front because a man that does like to rent pigs is... he's hard to stop - Gus McCrae