Mechanical Parts Suppliers

US

McMaster-Carr - A leading US supplier of raw materials and mechanical components.
Stock Drive Products - Huge range of mechanical components.
Servo City - Motors, gears, belts, wheels, drivers and much more.

Australia

Small Parts - Screws, nuts, bearings, materials, and tons of small hobby parts.

Netherlands

RVS Paleis - Stainless steel screws, nuts, drill bits & taps