its best you do that as an affiliate I guess, because Walmart's business model is more like a franchise, and for you to get this kinda business up and running, you really need tons of dollars (millions I mean). So if you don't have qualms raising that kinda money, I don't see any problems. Walmart is not like eBay and Amazon, where third party merchants like you and I can sell our wares to clients using their platforms. I stand to be corrected though
Walmart is American company mart. I think you just go there and talk to manager for buy a stall there.
If you have a specific type of goods, then you need to negotiate directly with the sales department. Walmart doesn't work like Aliexpress.
Walmart is not like eBay and Amazon and you will need a connection to get u into that store or even stay in that store. If you have a good invention apply for shark tank and a shark if they invest in you can 100% get you in Walmart if that is what you desire.