Here's a website you might find useful in your search for Scottish books! There is a monthly newsletter you can sign up for from them too. Each month there is an author of the month highlighted.
BooksfromScotland.com, based in Edinburgh, Scotland, is no ordinary
bookseller. Set up to showcase and sell Scottish-interest books, the site
combines bookselling and interesting, newsy content. With readers from Paisley
to Prague, and contributions from academics, authors, publishers and customers,
BooksfromScotland.com is the comprehensive e-portal for Scottish books,
literature and writing.
Their handy timeline for Books in Scottish History!
The link to their authors page.
Hope you find something you like!