Finally got parts for this one. I was able to get some glass from Bulgaria (this size is unobtainium in the US) and the other parts it needed from Germany. Thank you to all those who helped me with finding parts!
That glass is still an oldtimer since it was made in GDR well before 1990. Rasotherm was the East German counterpart to the West German Schott Suprax glass. So keep a good eye on it!
A great effort with the fettle, it looks lovely now. These lamps are a real pleasure to use when restored. Good work!