You could try Chessler's

http://www.chesslerbooks.com/eCart/searchItem.asp?strSearch=cho+oyu&=GO

Why? If you said why you were so keen it might be easier to direct you somewhere?

There's unlikely to be (m)any recent books ONLY about ChoOyu because no modern climber would write a book about just one climb of a popular mountain like ChoOyu, unless some major sexy disaster happened on it. An ascent by its normal route is considered the easiest of the 8000m peaks, so why write a whole book only about that?

If you're looking for first ascent info, Google "Herbert Tichy".

If you want climbing route info for the mountain itself, look at the Kielkowski guide, as seen at:
http://www.amazon.com/Cho-Oyu-Himal-Kya ... B000PS6H86 and
http://www.alpin-antiquariat.de/de/dept_184.html

D