Clive: I have almost finished restoring a B29, which also had very worn gears and would have I would imagine the same set-up as you need. I was put onto a chap who keeps a stock of gears for old english lathes etc which are still widely used. The tooth profile was the same and I was able to get the diameters and teeth numbers I wanted..then just a case of getting the gears slimmed down and the middle modified to suit. The chap operates out of a lock-up about 1 hr North of Sydney Aus and I can try to find his name, but try for lathe type spare gears first.