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Do you have some different National Rail TT to me?
I know the staff Working TTs have them in (I have a few copies myself), but the NRT that you can buy in the shops doesn't.
Also, try www.travelinescotland.com , despite it's name it gives train headcodes for all of England , Wales & Scotland, eg type a journey say Manchester to Stalybridge, and it will come up with somthing like 1E21 for example.