Comprehensive information. Including colors, numbers delivered per year, specials etc.
A wiki page with mainly technical information from US. The link brings you to an overview of the different pages showing information
The website is in German, but probably Google will solve that. Lots of information, practical, technical, how to modernise your car etc. Unfortunately searching may take time due to the language, but there is a lot of info available
Citroënet has information on all Citroëns and of course also on the SM. You can find quite some here.
Everything on Citroën SM in the US, differences with European cars etc.
if you want to reach me.Disclaimer: I take no responsibility for information or links on this site or the sites linked to.