I downloaded the .zip from https://www.arduino.cc/en/Main/ArduinoBoardDue, which contained a .brd and .sch files, but there was no .lib file. Where can I find that? Thanks!
-Janna
You don't need a library for any Eagle board. All of the part detail is included in the Eagle files. If you would like to use those same parts in your own designs, there is a method to export those parts into your own library file. I forget how, so I won't try to give instructions on doing it.