Hi - the most difficult thing to get right for this kit is the motor/propeller combination. We initially tested a variety of motors from Amazon and found that these worked well:
https://www.amazon.com/gp/product/B01N9ETA9Z/
but 1) they are no longer available and 2) the wires were too short to meet in the middle of the popsicle sticks when making the drone frame, which was annoying. So the motors in our kit are custom-ordered by our kit supplier with longer wires and unfortunately I do not think you can order them directly anywhere. You should be able to find similar motors on Amazon.
We ordered the propellers separately and found that these worked well:
https://www.amazon.com/gp/product/B079DP3V42/
You need to make sure that the propellers will fit onto the shaft diameter of the motors you order. You might also be able to find matched motors/propellers on Amazon, for example these came up in suggested products for the motors I linked above:
https://www.amazon.com/YoungRC-Coreless ... 078NL9KQQ/
Another consideration is the battery. Our kits come with 4xAA batteries which are cheap but drain rather quickly. That works well for an independent student science project, but for repeated use in a classroom environment you may go through batteries pretty quickly, and be better off with either rechargeable lithium batteries or a wall adapter (which need to be matched to the rated voltage of the motors you purchase).
Ultimately, you will need to build a drone and test to make sure that the combination of motors/propellers/batteries you have selected will actually lift off. I would recommend doing that before committing to buying enough parts for your whole club.
For the ultrasonic sensor, our kit comes with the HC-SR04, which is far cheaper than the popular PING ultrasonic sensor, and has comparable performance as long as you are measuring a flat surface, like a piece of paper taped to the bottom of the drone (the PING works better for smaller/irregularly-shaped objects):
https://www.amazon.com/s?k=hc-sr04+ultrasonic+sensor
For the transistor, most common N-channel MOSFETs are fine, for example:
https://www.amazon.com/gp/product/B07CTF1JVD/
For projects that use specific parts that are not included in either our drone or Arduino kits, the materials list will have a link to where you can buy the part. For example this project links to the joystick:
https://www.sciencebuddies.org/stem-act ... #materials
All of the other little parts (switches, potentiometers, resistors, etc) are pretty standard in Arduino/electronics starter kits etc, and do not really have specific requirements.
Hope that helps, please let us know if you have more questions!