The only source that I know of which is web-based is for the generic Boeing/Honeywell FMC stuff ......... which, if you're doing a 777 course then you will already have? It's at:
http://www.smartcockpit.com/pdf/plan.../systems/0011/
If you're after a published (real, live, hold in your hands book!) version I only know of 'The Big Boeing User's FMC Guide' (757,767,747,777) by Bill Bulfer and Richard Gifford. The home website is:
http://www.fmcguide.com/catalog/index.php?cPath=22
I have not seen a copy so I do not know how good it is .... but it does look weighty. Happy hunting!