Fwiw, at one store, I found three inside the store in the garden center boxed and sitting on the shelf. At another store, I found 3 that were unboxed and assembled, standing in a "heard" of sorts with other outdoor cookers.
Also, be sure to try and look up in the rafters. Lots of the outdoor stuff was put on skids, that were plastic wrapped then put up high. They then bring the skids back down and are trying to unload last year's stuff as they reset for grilling season.
All that said, it's entirely possible that inventory counts are off for any number of reasons.
Other little tricks. If you have the Walmart App, open it, set "your store" to the one that supposedly has stock. At the BS page, find the link to "View on Walmart" and click it. It should open the Walmart app on your phone and tell you where the grill is located. Should even display it on a store map.
Additionally, on the BS page, there's a link to "view barcode". Pull that barcode up and try and find an employee with a hand held scanner (Not just a phone). I simply walk up and ask "Do you have the scanner thing that tells stock level and location" ? have them scan the barcode. The results page will tell what the computer lists for amount on hand to sell, and it might list it's bin location.