@drhf : In Germany, it is available through all bookshops that are connected with their online shop to one of the wholesale traders (Libri, KNV,...). Which is basically all bookshops :-). I'd check the big chain stores in your country, they will probably also offer the discount for the epub version of the book.
(I always check at my local bookshop's website, if Amazon offers discounted books, and very often, the epub is discounted as well)