Below are some of the places that we use for purchasing kit and game field components.
McMaster Carr -
Home Depot - PVC, plywood, etc
Lowes - PVC, plywood, etc
Westbrook Metals - aluminum (cut to size)
Allied Plastics - plastic sheet
Stock Drive Products - belts, pulleys
National Precision - bearings
Bearings Direct - bearings
Bike Parts USA - inner-tube, etc
Northern - miscellaneous parts, lights
Mouser Electronics - switches, chips, other electrical components
Digikey Electronics - switches, chips, other electrical components
Online Components - switches, chips, other electrical components
Dymond Modelsports - R/C gear, etc.
Tower Hobbies - R/C gear, servos, batteries, etc
VEX Robotics - controller, motors, etc
igus, Inc - Plastic components: bearings, cable guides, etc.