I'm not looking for just stories, but actual books, fictional stories in paperback or hardcover.
To my knowlegdge there aren't any to be found, at least like those you find posted on-line.
The closest you get to the buffed chix topic is either those rare instances in sci-fi - "Friday" by Robert Heinlein or S.M. Stirling's Draka Trilogy, mainly in the third novel of the series "The Stone Dogs" which does get femuscularly graphic in a couple of instances. If I recall correctly, Lingster reviewed one of Stirling's more recent works on his blog page last yr for its femuscular content. It might have been "The Sky People" or "In the Courts of the Crimson Kings" but I'm not certain.
Or in exposé works about the world of FBBr - "Chemical Pink" by Katie Arnoldi being one of the more recent covering the more unsavory elements that gravitate about the physique sub-culture.
As a buffed venue for hard copy storytelling, the subject is generally more commonly found within the realm of comic books - She-Hulk or Powergirl as recent examples. You also might want to check the thread here at Amaz0ns about Lyman Dally and his Quadra Blu character.
EL Publications was a source for comic book graphic growth novels, but I heard had gone of out business. Some of their materials might or might not be found on eBay.