Bottles

I've been searching for bottles that I used to see everywhere but I can't seem to find them anywhere. They are the kind that are pretty much open on the bottom and you put the bag in and push it up before you screw it in so the baby doesn't get air. I've seen them for the breast milk bags but I'm just concerned about finding the regular ones in case I can't keep producing milk. Does anyone know of a brand that sells them or something like them?