Most of the .50BMG ammo I shoot is military surplus and headstamped LC 08 & 09.....a lot of the WWII (30's & 40's)and Korea (40's & 50's) ammo is for collectors. Have you actually seen cases recently marked 43, 44, etc?
Midway, Natchez, Cheaperthandirt, bulkammo.com, if not in stock, will notify you via e-mail that XXX ammo is available. I recently got an e-mail from one of them at 2:08AM that 5.56 was available...ordered 1k rounds at 2:50AM (wake up time anyway), texted a friend about it at 3:30AM and they were already sold out.
You have to be ready to pull the trigger (pun intended) when you get the e-mail. We put 1k rounds away for each firearm we would keep when war breaks out in the US so the rest is just for shooting. I have supplies enough to reload another 2k rounds for 12 ga, 9mm, 5.56, and 7.62x39 (cases, hulls, powder, primers, projectiles, and shot). I have a lot for .45acp and .44 mag but they won't be with me when the time comes.
This happened in 2009 also but I think it's worse this time....I learned my lesson back then and stocked up (yep, I was one of the fools that actually paid $1 EACH for .380 back then!!!!) and I store it sealed in ziplock bags and gasketed military ammo cans. 7.62x39 remains in their sardine cans. Brass handloads also get a smear of poly over the primer and around the case mouth. 12 ga gets a smear across the primer and a little wax sealing the crimp. Overboard? Yep! That's me!
If the ammo situation doesn't improve, just wait a bit longer and you'll have plenty to choose from off the bodies laying around.