I've had the same experience with wal mart.
There is one close by my house that I check every time we go for any random thing. Haven't purchased anything in months.
This morning I swing by because I was picking up a for sale sign. They had 2 50 rd. boxes off WWB .45 auto so I knew they got some stuff in.
I ask the girl and she says no they don't have anything I asked about. Then she says, "Wait a minute. You've been in here a lot..."
Poof! Out from behind the counter comes 1 20 rd/ box of tula steel case .223 for $5.72!
Of course I bought it...
Then she tells me the exact days they get the truck... I can't share that info, but this wasn't the day and it was 10:30 in the morning when this ammo magically appeared.