I wanted to use the Tinyflex Bowden Extruder to start playing around with flexible filament, but it was impossible for me to find the 30mm spring required, so I remixed it to use the 20mm spring that's widely available on almost any site that sells 3d printer parts.

For the hobbed gear, google "Hobb-Goblin 5mm/8mm ID Drive Gear" or get it here