I think it is gone. It was on his site for light yrs, but I checked and it isn't anymore. Possibly went to another Wicked enthousiast.
Heylight does still the 'Sattlestutze mit Versatz'. Already for around 15yrs or so, so will be pretty much period correct. They do every size or colour you want. Cost less than a Thomson. Other approach is a USE with shim? Searching eBay for a while?
Location: No, I am not in the Dutch mountains. I am at the North Sea coast, near Schoorl. MTB'ing is good overhere, in the dunes.