Hi Frank, Pavel Simek should have some parts for the gear change gate, so you would have to finish it. You can find his contact in Yowl at the local section contact details page). I made some drawings and dimensions of the gear change lever for Zoran Vaskovic, so I could resend you the photo, if you wish to make it. If I remember well, I think Alan Noakes made gates as well, I’m not sure if lever as well.
I don’t know if it’s possible to buy ready made bowdens, but I bought the bowden, steel cable and soldered the endings, it was also easier to make the lengts as I need. And they works well, I did over 18000 km and soldering holds perfectly.
All the best, Martin