I do not believe there is one. I climbed Cho Oyu last year and spent time in the Kathmandu bookstores looking for a Cho Oyu book. the closest thing was a book that combined one European climbers account of climbing Everest and Cho Oyu, but it had few pictures and didn't look very interesting. It did, however, come bundled with a map of Cho Oyu, in some of the book stores.