Hi
I've often found Scot-Rail.co.uk very useful for making Scottish scenario's. Plenty of useful information on all things train related in Scotland.
One scenario I made recreating the Loco hauled Fife inner circle (available on Mully's site) is my favourite of all scenario's I've created due to the amount of accurate numbering and liveries I was able to add. All it took was a couple of hours of research on Scot-rail to gather all the info I needed.
You do need to register with the site to access some of the information but that's all it is, registration, I've never heard a dickie bird from them otherwise.
http://www.scot-rail.co.uk/page/HomePage
Any other similar sites covering other parts of the country, feel free to add post them.
Regards
Phil