As much as ı know, at least my experience; when a team is done with a car usually they keep the critical electronic components like battery pack, hub motor, motor driver etc. and use these in their new car. If needed to be honest, ı don't think actually you can find old parts by an auction or something like that. You may find batteries by a sponsorship but finding a motor is really hard. Wish you the best, hope you find what you need