Who put the new string on? Why have they not replaced it?
knockpoint did and they can't find it, and apparently can't get some new one
I've heard they're a good shop. I have a hard time thinking they'd just brush you off. If they persist, tell them you'd either like them to produce a string stop or a replacement bow - their choice. I had an aftermarket stop put on my Hoyt Turbo Hawk, which was made without one. There's got to be a solution they can come up with.