When I looked for a propeller guard for the Crazyflie 2(!), I found just one - and that turned out to be too big for my 3D printer. Thus, I simply made my own using OpenJSCAD.
Please keep in mind that you need four of these in order to protect each propeller!
Simply push each guard onto the motor and let it snap around the motor arm - that's it! If you need a stronger fixation, you may additionally wrap some tape around the clip.
The OpenJSCAD script is also available for download - just open the "Thing Files" tab!