I've been looking for a 26tpi headset, new.

A place called Marleen Wholesalers lists model AR01, 22.2 ID and 26 TPI - they confirmed this, but...

"Unfortunately we will not be able to help you out sorry – we do not sell direct, but only to bike shops, and only within New Zealand. (maybe you could contact a bike shop here in NZ and see if they are able to ship internationally?)"