I had this problem recently. Walmart puts their overstock of WWB ammo in common sizes (9mm, .40 and .45) under the counter on the side where the register is. They may have an empty spot on the shelf behind the back of the clerk, but their may be more under the register in those locked shelves. If you can, go around to the other side and look there first.
Also, they've got the cheapest 12 ga rifled slugs and buckshot that I've found. it was $2.38 for 5 1oz winchest super x rifled slugs, and $8.82 for 15 rds of 00 buck winchester 12 or 15 pellets (can't remember). Bought all they had yesterday, and will continue to do so. Sorry to anyone who wants 12 ga buckshot at the Newton, KS walmart, better get there before Sunday afternoon when I do my grocery shopping.