Headcodes are listed in a lot of places.
The Scot-Rail website has headcodes for almost all Scottish trains, and although these are not up to date, I would imagine that they haven't changed much (as the timetable is similar). Some headcodes are up to date, and the others could be easily done I would imagine given the wealth of knowledge on there.
This page also had some diagrams, but these are now out of date again and son't seem to be getting updated any time soon.
The only other page I know of is
this one. Some have been updated here, whilst others haven't.
Diagrams sometimes take a wee while to come up, and tend to change with each timetable. It's unusual to find a new diagram up on the internet until a few months after each timetable change, and some don't seem to appear at all.
