A quick check of the Home Depot site shows many stores with high inventory (80-100+ per store) of the 2-gallon MA packs, so that's where I'd go. They don't show the inventory count of liquid chlorine, just say to check at the store, so I can't help there.
I haven't read anything about a muriatic acid shortage (except a couple questions here) -- are there places where it's hard to find at places like Lowes/HD that show their inventory? I wonder if some pool stores aren't getting consistent deliveries because it normally comes on the same truck as the liquid chlorine, and those deliveries are being disrupted?