Ian,
Given your location "North Norfolk", you might want to pay a visit to the North Norfolk's diesel gala on My 25-7, when the DPS are there with 55019.
My guess is they will have a sales stand at the event either on one of the stations (Sheringham?) or on board the trains.
We'd certainly be doing that if we were in attendance with D9016 and/or 55022 (afraid we don't stock the book!).
I don;t think you'll have any issues with a postal purchase from the DPS ny writing/sending cheque, just as long you remember it's all done by volunteers, so don;t expect immediate dispatch. Think they've recently changed their sales officer.
From what I recall of flicking through the book, would imagine it'll be invaluable for you. I don't know if you're a member of the Deltic Yahoo group, but seem to recall someone posted some track plans and things some time ago which might be of help.
Good luck with it is it sounds a great project!
Dave