I forget which part of the US you are in. But out here near the west coast, stores sell what must be the same thing. If these were available when I was active, iguana keeping would have been easier. I suspect these bags are filled with nitrogen before they are sealed, which would explain why they last so long. Also notice that there is no liquid water in these bags, which also extends their shelf life.
Kale has a bad reputation now, and it shouldn't. It has it's place in our iguanas' list of foods.