I remember seeing Newark Street Starfire bass thumbrests on ebay and possibly on reverb when the line first came out, but I can't find any now. They do (or at least did) exist for aftermarket purchase. However, they're not exactly vintage spec. A fellow LTGer bought some for his vintage jetstar and the screw holes didn't line up. If that's okay for you though, he may be willing to sell them to you? Don't remember off the top of my head who it was, but if you use the search function on here the thread should pop up