Hi Iain,
I have purchased several books from the NLS and although the service is good I do atest that it is somewhat expensive as Gordon mentioned.
Here's a cheaper alternative:
http://www.abebooks.co.uk/servlet/SearchResults?sts=t&y=...1. Walter Wathershanks' Adventures at Lammas Fair
Bookseller: Last Century Books
(Innerleithen, ., United Kingdom) Price: £ 20.00
[Convert Currency] Shipping within United Kingdom:
£ 2.75
[Rates & Speeds]
Book Description: George Lewis and Co., Selkirk. Soft Board. Book Condition: Near Fine. No Jacket. 12mo - over 6¾" - 7¾" tall. Tammy Clinkscales's Adventure with a dog. An amusing Sketch by the same Author. illustrated booklet. pp 56 Amusing Borders story. Excellent condition having been in storage for many years. No date. Looks early 20th C. written in Border tongue. Staple-fold Booklet. Bookseller Inventory # 003445
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Regards,
Larry