goBILDA is the main reasource that we have bought parts from. Everything from the wheels to the metal frames are from the site. Other than that, the only hardware non-goBILDA is the 3d modeled hood on the robot:
Link - www.gobilda.com
The second source of parts were REV robotics, they sourced parts that control the motors, such as the driver and control hub.
Link - www.revrobotics.com