I asked in a Reddit thread for tips and someone suggested the Hot Stock app.... it sends you alerts when things go in stock, and if you pay $5 a month you get alerts ahead of the rest of the users.
So I tried it, and every time I got an alert, I STILL couldn't get to the sites fast enough to get one through checkout. Until yesterday when I managed to buy one at Walmart.com.
Then this morning, the order got canceled. I chatted with their customer service to ask why and they said that it was a duplicate order. So I checked and I didn't have to orders. They said it was because someone else at my address bought one.
Turns out, their algorithm isn't smart enough to recognize apartment numbers, and one of my neighbors in the other apartments in this building bought one.
They said I could re-order... which is nearly impossible, and if I did it would just get canceled again.
A half hour after all this, I got another alert, this time CostCo, and I was able to get an order in through their app.
Fingers crossed that it actually ships.