There are a few companies that will make replacement springs, they advertise in old Bike Mart. Alberta Springs in Colchester ( 01473 311783) is a aname that comes to mind. If you send them both parts, they should be able to make you a replacement.
As for the coils, I have had them rewound by West Countr Windings in Thetford, they did an excellent job with a fast turn around.
I have had a couple of Stornellos converted to 12volts by them. I had the top coil modified to convert it to 12 Volts. Have a read of the comments in this thread.