DC Motor Servo Motor in Education Classroom pack

I noticed one of my students doesn't have all the parts for the servo motor. Can anyone steer me to the right replacement parts to purchase to ensure they can do the projects with the servo motor. They are missing the plastic rotors. Thank you!

Exactly what kit/product is this?? There are many.. Link?

We have this

Did the kit arrive with missing parts, or did the student lose them?