Stu,
Nice area for riding, I really like Poole.
I don't know about alternator rebuilds, I did search and couldn't find anything. I am not a techy(unfortunately), but if you post a new topic in the tech area you will get lots of responses!
What bike do you have, I assume it is a DOHC?
Also, is this what you need, they are available on ebay for 30 quid.
Jim.