In my experience, the only ammunition which Walmart can be counted upon to have in stock is the very most common calibers. For handguns, that means .22LR, 9mm, .380 Auto, .38 Special, .357 Magnum, .40 S&W, .45 ACP, and .44 Magnum. There are some that will also carry calibers like .25 Auto, .32 Auto, and .357 Sig, but those are a bit more hit-or-miss. Once in a great while, you will come across a Walmart that carries a connoisseur's cartridge like .41 Magnum, 10mm Auto, .45 Long Colt, .44 Special, .454 Casull, or .500 S&W, but those Walmarts are few and far between.
It has also been my experience, however, that 10mm ammo can usually be found in about any decent gunshop as well as some of the "big box" sporting goods stores like Cabela's, Bass Pro, and Gander Mountain. If that fails, 10mm is certainly available from online retailers like Midway, Graf & Sons, Natchez, and Sinclair as well as smaller ammo vendors like SG Ammo and Ammunition to Go.
If being able to buy ammo at Walmart is a criteria for you, you'd be best served by sticking to one of the cartridges in the first list that I provided.