ski pylon question

Hey guys when I bought my prostar 190 it didn't come with the slalom ski pylon and I want to add one. Does anyone know where I can get one? I could make one but I can't figure out how it mounted in there. There's a semi circle for it to sit in and a couple holes that look like they're for a U-bolt but that won't keep it from sliding up or down just forward and back. I could jimmy something to make it stay but aren't they supposed to be height adjustable? Also If someone could give me an idea of how tall they're supposed to be that would be awesome. Any help is greatly appreciated.