Have you looked at Luisi bosses? Autobella supply them in the U.K. They do one that fits a S2/3. Might be worth seeing if they fit your wheel.
I had found them in my search, unfortunately as far as I can see they only make a boss for newer wheels with the 70 or 74mm PCD - the cost of the boss and an adapter to fit my wheel is over £100 so I'll hold out for something that directly fits if possible. I like my wheel but maybe not that much!