I have aquired a dead Hayterette with the 2-stroke Villiers Torquemaster engine. All seems to be in reasonable order, other than the coil which is dead. The part number is M.2576.E. However this does not seem to be commonly available. Plenty of similar after market coils for the motorbikes, but not similar enough to be a straight swap. However with a little bit of work it may be possible to modify one. The overall length of the "Long" motorcycle type is the same at 2 inches, but the motorcycle coil is slightly fatter, and has a larger diameter core. As the existing coil is pretty close to the rotating magnet, a slightly fatter one is likely to rub.
Now I have a lathe and a crazy plan... but no it is not to try and turn down the overall size of the coil!!!
If I were to turn down the ends of the iron core to match the size of the old coil, but do so eccentrically, I would gain enough clearance to fit the larger coil without having to modify the coil itself at all. This will be a a lot easier if it is possible to remove the iron core, but if not I think could still do it without the coil itself coming to harm.
Any merit in this idea, or am I going to just have to try and find the correct replacement and cough up a large sum for the pleasure?