It is going to be hard for you to find a replacement screw for that, since it was only made in the year 1970. I would search Ebay. As for the gold coming off, it is electroplated with 18k gold, so maybe your local jeweler can replate it.
I was hoping since it was designed by the same person as the Cartier Love Bracelet it would have the same screw size. Unfortunately I have not been lucky enough to find JUST the screw online anywhere. Maybe a jeweler will have something that will work!