My experience: There are 2 walmarts near WDW. Both in Kissimme, one on 192 and another on Osceola Parkway (I think). Though it is the closest to WDW, avoid the one on 192 - always crowded, difficult to find parking, too many traffic lights from WDW.
The one on Osceola Parkway is a super store and is not crowded. Farther from WDW but you can reach faster. If you need exact location, go to walmart.com and click on Store Locator.