I just got back from the Wally World on Fairmont and Carter's Country, the Wally World was almost out of ammo. Just a little 22, bird shot, and a few boxes of hunting loads. Carters Country was real low on 223 and other military rounds. They were low on pistols but had a 6 AR's in the rack.
You should try Tomball Pawn. I was there on Saturday, and they had a chest-high stack (cases) of 223 (Winchester?) and a waist-high stack (cases) of another brand. There were several thousand rounds of FN 5.7x28, and multiple cases of 308 (200 rounds per case). There were also a couple other cases there, but I don't recall at the moment what was in them. That is what was stacked on the floor.
They also have other cartridges (mostly pistol) in smaller boxes on a shelf behind the counter, but not in such high numbers.
I went to the Academy in Pasadena today (12:00pm). they had 5 boxes/ea. of .40cal (black box) and 38 spl., not sure what brand name. IIRC the price was $24.99 for both calibers. The thing that caught my attention was all the boxes of monarch boxes in 223. This is the second Academy I've been to that had plenty of 223 ammo. They had about 5 to 7 boxes in the light blue box, too.