You can get them direct from :
18 Hillside Road
The Caunter Scheme 1940-41 (desert colours in North Africa): £8.00
Alamein and After 1942-43 (desert colours to the end of the desert war): £10.00
Sicily and Italy 1943-45 (colours for the later campaign in the Middle East until the end of the war): £10.00
British Army Colours & Disruptive Camouflage in the UK, France and NW Europe 1936-45 (France 1940, Normandy to Germany 1944-45): £10.00
Postage and Handling outside of the UK is £2.50 per book.
I also know they're available from White Ensign Models
along with the matching Xtracolour enamel paints (if you're a Vallejo user you can easily mix/match the vallejos with the actual colour chips the books include) for approximately the same price per book.