At my store they are 2 blades in a little plastic bag sort of taped over with a hole on the top to stick on a rack. Once I found one that had a cardboard label.
It's really easy to overlook and some stores don't get them in often. Or get very many when they do come in. I'd call to make sure they had some before making a trip if it's a special trip. I just stop by when I'm at the grocery store next door.
I've been thinking about buying the actual carpet cutter and just throwing away the yellow plastic thing. But that seems so wasteful...but hey $3 for 3 blades, not really in the whole scheme of things.