Classroom Resource: Ordering Spare Parts
This EV3 page on the LEGO Education site allows ordering of some EV3 parts:
https://education.lego.com/en-us/shop/mindstorms-ev3?replacementparts=20
However, often the desired part is bundled with other unneeded parts (some not even from the EV3 Education Core Set).
This link allows you to order individual parts by specify the the kit number you are interested in (#45544 for the EV3 Education Core Set):