Bloke called Mitch. i forget the name of his operation now; somewhere Midlands-S-Yorkshire-ish. Haven't seen him around for yonks either...
I've never seen a single electric winding mag. Needing batteries, sound control pcb and motor in there, there wouldn't be much space for BB's...
You can get a little hand unit with a motor in it that you hold against the wheel of an ordinary hicap and push a button to wind - £18 IIRC - although I can see that turning into more of a pain in the arse than winding lol!