I was thinking the same thing as the OP. For example, I noticed that a few weeks ago I couldn't find any of the popular calibers at the local Wal-Mart and very few even online (i.e. 9mm, 7.62x39, .223 Rem). However, less mainstream calibers, such as .32 ACP, .45 GAP, and 7mm Rem Mag were still available in quantity.
This has caused me to rethink my SHTF stockpile as far as actual guns are concerned. Previously I've (mostly) concentrated on buying SD guns in one of four different chamberings: 9mm, 7.62x39, .223 Rem, and 9x18 Makarov. Given the reality of the current ammo supply situation, which is a good real world example of what a prolonged SHTF situation will do to our ammo supply, I now think it is a better idea to have a variety of SD guns in various calibers, simply due to the fact that ammo is available in quantity for less popular calibers during this shortage.
I will maintain my current stockpile of the big 4 calibers, but if find a gun that I like isn't in a popular chambering, I'll still get it because its actually easier to find ammo for it now than for a popular caliber.