From what I remember, 7-Eleven considers itself too special to carry these. When I've seen them, they've always been in, like, weird off-brand truck stops and gas stations that aren't part of a chain.

I used to get them at a local gas station back in like 2005. They were 99 cents, and you could microwave them right there in the store. They weren't good, but it's a cheap and quick way to get ~800 calories in you.