It's available in all good book stores, or at least it should be but, as I'm learning, it is harder than you think to get into bookstores. If you can't find it please ASK their helpful staff. They will be able to order you a copy and it shouldn't cost you any more. You can also order it on-line from on-line retailers like Mighty Ape or FishPond.
(PS - Because I'd hate you to miss out, it is also available in most public libraries. If your local library doesn't have a copy get them to order one!)
It is being distributed by IngramSpark and Publish Drive and they have links to 1000's of book retailers like Amazon. It is available in the very popular Kindle store. You can even buy it and have it delivered free to over 160 countries - how good is that! The Book Depository is one you can try.