At the time I was looking the only sellers were from the US and with the shipping rate of around 60 USd I could have a new fork with 22.2mm plus adaptor instead.
Luckily I found a nice 21.1 quill stem from a LBS.
Sorry to heat. I stumbled across them on accident. BMX bikes used the 21.1 standard. I'm an early MTB fanboy and they are not at all uncommon on those bikes.