Hi Ben,
Stewart sells the book through his website and I don't think it is available through stores. If you contact him through his website he may be able to work something out. At the very least it will cut down on postage. I have attached the web address below. It also has the covers of his soon to be released books.
http://www.redfernnaturalhistory.com/
I don't have the ISBN handy but if you would still like it let me know and I will check the book and post it here.