For anyone who wants one, you can order them here.
I still think the name is horrible(where I'm from, a zip gun is a cheaply made gun; usually made from scrap material found around town, that's designed to specifically commit crimes then tossed) and it seems so impractical in every way. The only rational purpose I've seen for this is what Double Naught Spy said and I don't think a 22 would be even decent for finishing off game that something larger couldn't do at range.
How did I forget the link??
Gallery of Guns