I asked a related question about 2 months ago.
@dk5sm5luigi responded with the site his team FRC1735 created: https://findrobotparts.com/
Also, about a year ago, there was a fairly long thread in which people shared what they like to 3D print for the robot: What are your favorite 3D printed parts for FRC?
Beyond that, if you go to 3D model download sites like Thingiverse & Printables and search for “FRC”, you will see plenty of interesting results.
Good luck!