S&W 3Gens are in that situation, a .45ACP mag is becoming harder to find, and the shorter compact mags definitely so. Yet originally there were about 3-5 each available as issue to every cop and the public bought just as many if not more.
Peruse the gun auctions and you see them supplied with one or two - the more resourceful gun stores sideline the rest and put them up for sale separately at the going rate. So a gun sold to them with five mags becomes a gun resold with one and four of them are listed for $45 apiece.
Secondly, reading forums you get the idea there are folks buying up every old mag they can. It's like the .22 craze, their are more mag buyers than the market can sustain. Posts with pics show 35-50 magazines in the hands of an owner of two or three compatible pistols. Why? "Because they aren't making them any more." And these are the same guys culling their collection of mags selling off the duds for the high prices. What was service carry of three to five mags rotated when on official duty becomes 10 -15 mags for a day at the range shooting their old collectible. Because they don't want to reload just a few constantly or put that much wear and tear on them.
There is also a distinct difference in application one army to another with mags - the Russians issued three AK mags per soldier and in peacetime that's all they got. They made do with them. In America the supply sergeant hands out dozens but you turn them in at the end of a range session. In combat dozens more. We are more used to having lots of mags for high capacity guns and we are willing to find and get them. In other countries it's not considered necessary or even possible. Goes to a shooter's mindset and what they are used to.
Am I saying there are hoarders of mags, not quite. But someone with 10-15 for one gun at the range does look like he's blessed with abundance when I'm down at my station trying to figure out how to cut a mag catch in a 1911 mag for a S&W 4566 and get some more shooting time compared to loading time. The only issue right now is good 1911 mags are just as expensive as S&W. In a few more years when originals pass $65 I will rethink it. Beats trying to tweak ProMags into a semblance of reliability.