The Google Books Lens can currently be found in a PPA by its author, and currently have a note that
These builds may have bugs, be unstable, try to eat your kitten.
To install add the PPA
ppa:davidc3/books-lens (How to Add a PPA) and then install unity-books-lens from the software center.
After this, you need to log out and log back (or run
unity --replace) in for the lens to show up and work correctly.
The lens uses the shortcut Super-b to show the lens.
sudo add-apt-repository ppa:davidc3/books-lens
sudo apt-get update && sudo apt-get install unity-lens-books