If you want older timetables, many working timetables can be found second-hand at bookstalls at swap-meets, railway fairs and the like. Shops on preserved railways can also be fruitful sources if they deal in second-hand books as well as new. The National Archives also have many that can be consulted.
But I regret I'm not certain how you get current ones - the information is usually considered confidential and employees are discouraged, it seems, from spreading it about.
Sorry I can't help you further.
By the way, I think your query would have got noticed in the Prototype forum - there was a fruitful debate about milk trains several months back which included WTT information.
I knew i'd seen one somewhere!
The book is called freightmaster...the national railfreight timetable.
Not sure how much detail it goes into but it appears it comes out quarterly.
The advert for it is on the back of railways illustrated but may be in other mags as well.
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