In my experience Walmart can be terrible about keeping these in stock---incredible when you consider it's a $15 sale, a tiny item easy to stock and it can't be stolen since it has to be activated at the register.
Re Gamestop, in my experience they're even worse. The last time they offered the $5 off deal I hit all 4 Gamestops within 10mi of my home and not only were they out of stock the clerks were clueless about their existence.
Walmart clerks are clueless too, of course. I always bring an expired card with me since one picture is worth a million words especially with these guys. Then I just point and grunt, and they grunt and point at an aisle and communication is complete!
Seeing how Walmart is considered the "greatest" retailer on Earth, as a businessman, I marvel at the ineptitude of some of their employees and the incompetence of how they handle keeping an item like this in stock. I've also had their website tell me certain stores had "x" in stock and when I get there, they're not only sold out but the clerk says they haven't had them in weeks. What's the point of purporting to maintain RT inventory status on a website and then have it not work at all?
To confirm when my local Walmart was opening on Black Friday I went to their Facebook page. Boy, you do have to give Walmart a certain amount of credit for enabling reviews on Facebook. The customer reviews of this store are BRUTAL, particularly about customer service and returns. Of course, anyone making a return at Walmart is going to be aggravated. I think working that desk is punishment duty for clerks who have committed a rules violation.
Long story made short: I absolutely DETEST shopping at Walmart and the only reason I go there ever is to buy SC cards. If Gamestop did stock them locally I'd never have to cross a Walmart threshold ever again. Oh joy!