The impression I get is that this current "banic" is buyers' panic provoked by anti-gun rhetoric for draconian restrictions in the media from politicians and opinion editorials -- the actual source of fears of gun restrictions. Anyone remember the NY bill to restrict gun owners to buying one magazine load of ammo every 90 days? That kind of thing prompts fear, uncertainty and doubt.
The OP talks about a two year supply. I was prompted to stockpile a five year supply in the late 1960s, prompted by having to find an FFL (mostly department stores with sporting goods sections) to buy .22s with the sales entered in the dealer's bound book by my name, address, DL number, make, caliber and quantity. Now that I am involved in matches at the local club, my stockpile is deeper.
The gun control advocates on the floor of Congress and the option editorials in the media calling for restricting or banning guns and ammunition had a lot to do with instilling my fear of federal restrictions or bans on ammunition. It was not instilled by the NRA, or dealers, or gun show promoters, but by me listening to crusading advocates of ever restrictive gun laws promising bans and restrictions and me taking them at their word.
It used to be that I bought guns and ammo at the sporting goods section of department store like Wards, Sears, K-mart, Penneys, Western Auto. No more. The last hold out in general department stores is WalMart and they're under siege. Guns and ammo have been ghettoized, removed from the mainstream, into dedicated gun shops and sporting goods stores. (As a cultural sign of the sigmatisation, marginalisation and demonisation of the "gun culture", in the original Dawn of the Dead 1978 there was a gun shop inside the mall; in the modern remake 2004, the gun shop was across the street from the mall in a seedy building.)