That is 100% completely butt-end backwards from real life, GAMEOVER44.
If you are looking for a caliber that still exists on store shelves or internet websites when SHTF
do not choose a 308. (Or a 9mm, 45, or 223; any military / LEO caliber is going to be gone, gone, GONE, and first!)
I could find 303 brit, 30-30, 7mm mag, 300 STW, etc, on store shelves, but for a very long while there after SH, there was simply no 308 to be had anywhere on any shelves, period. 30 cal reloading components from 150 through 220 grain were also scarce as hens teeth for the better part of a year, too. I waited nearly 7 months to get a backorder filled on 220 gr sierra MK's. (Then ALL of the backorders I placed trickled in one by one and now I have enough for the rest of my barrel life and then some)
Anyway.. yeah.
Conventional wisdom is "get a caliber that everyone uses"
But that's the problem. EVERYONE thinks that way, and as soon as there is a problem and the great gun-culture herd panics, they trample down the gun store aisles and buy every common caliber *anything* that isn't nailed down.
And each time it happens, it gets worse!
You want to play it smart, buy an oddball caliber. You can keep shooting when everyone else is busy hording the common stuff and panicking.