So I had picked up a second M900 a bit ago for my wife, Milli, to learn to ride on and hopefully share the hobby with her. I picked a fixer-upper so that should it get dropped, nobody could be too upset. Its got a variety of maladies, some of them electrical.
So I did what I almost always do when looking to solve a problem, and that is to learn a lot of somewhat irrelevant information.
Here's my short list of places one can get electrical parts for our bikes (omitting aftermarket parts like turn signals and taillights, etc):
Electrosport.com - Regulators
Ricksmotorsportelectrics.com - Regulators, Starters, Starter Rebuild Parts, Stators
CA-Cycleworks - Coils, CDI Replacement Ignition box (Ignitech), K&S Switches to replace handlebar switch sets
Dyna Online - Dyna Coils and Mini Coils
Silent Hektik - Complete ignition systems, coils
Post up if you come up with any others
http://www.electrexworld.co.uk/ducati-road-motorcycles-electrical-parts-1259-0.html (http://www.electrexworld.co.uk/ducati-road-motorcycles-electrical-parts-1259-0.html)
http://www.ignitech.cz/english/aindex.htm (http://www.ignitech.cz/english/aindex.htm)