There's a new book on Brokeback Mountain which is due to be released in November. Here's what I've been able to find out about it:
Annie Proulx's Brokeback Mountain and Postcards (Continuum Contemporaries) (Paperback)
by Mark Asquith
"Product Description
This title presents an accessible and informative introduction to two texts from one of America's most experimental and provocative authors. This guide to Annie Proulx's novel "Postcards" and her short story "Brokeback Mountain" features a biography of the author, a full-length analysis of the texts, a summary of the their popular and critical reception, a discussion of the recent film adaptation of "Brokeback Mountain" and its reception and a great deal more. If you're studying either text, reading them for your book club, or if you simply want to know more, you'll find this guide informative, intelligent, and helpful."
Apparently it can be pre-ordered from Amazon.