I'm not sure where you can find these, but Fischer sells 22oz flip top bottles - I dont know about a 4/6 pack of them though. Grolsch flip top 4 packs are about the closest thing actually seen states side.
I do not know where you are. If you are any where New England, Otter Creek from middlebury VT. has 4 packs of it's "world tour" special beers. That is, 4 22oz. bottles.