I've written a bookmarklet that enables you to see if the book on the page you're looking at (at Amazon for example) is in a library in Buckinghamshire. I've adapted the work done by Jon Udell on his LibraryLookup page. To install it, drag the text below to your links toolbar.
Then when you're on a page which has an ISBN in the URL click on it and it will create a popup window with a search for that book in the Bucks libraries. If you want more guidance look at the videos on Jon's LibraryLookup page.