As a temporaty measure until the right item comes up it might be possible to get a common (and cheap) amal float and adapt it to work on the B&B? So long as it fits together ok you'd just need to change the float height.
I do keep a lookout for B&B carbs at jumbles and on ebay and they do surface quite regulary. They don't go for peanuts of course but they are not superstar money either. The smaller 2-stroke types seem to come up the most and their floats look similar to the larger types and I have a feeling that they can be put onto the slightly larger carb that the EW will have (maybe someone can correct me on this?)
I know of some people who run their vintage machines using a modern mikuni with an adapter. I'm not sure that this works out any cheaper in the end and with the Douglas being so easy to start there is less need than on a Gold Star or Velo for example.
You could also try Paul Milner (pnmilner@yahoo.co.uk) who is not cheap but does have all kinds of unobtainable goodies. You could also try Ron Farthing (info@RonFarthing.co.uk) also not cheap but worth a try.
