I've one of those generic ETC branded seat posts in black if it's any good? It's as new with just a little bit of marking at the absolute bottom, well hidden by the frame. It's looking like I need 26.6 for my own project, despite all the research I made suggesting otherwise :facepalm:
It's a nice long 400mm one as well, which might be useful for an early Bonty - in my experience they like a long post as they can crack around the seat collar area if you're unlucky.
Appreciate it isn't super high end but it would get you up and running in the meantime. You can have it for a tenner posted? I can ping pictures over later if needed
More bad news now as the only suitable ones I have are unbranded. I had some nice branded ones I was thinking of when I replied to your thread but the memory isn't great ATM and they were the wrong diameter. But they weren't Syncros etc anyway