I am looking for a certain type of knife...?

Its like a stiletto switchblade, but doesn't come out from the side, it comes out from the top. I used to have a NATO one, but can't seem to find one on Ebay. Push the switch up, the blade shoots out, push the switch down, the blade retracts in, and it all happens really fast, what kind of knife is this and where can I get one???