Solution: The user is given an option to mount their kindle as a removable drive, and further to drag/drop all of their ebook files onto the page. I then parse all the file names which contain the ASIN. Using the ASIN, I can search Amazon for the book information including if it is lendable or not.
This is not exactly what I was hoping for, but it works good enough. If someone comes up with a more eloquent solution, I would be very interested!