This is a design of the RepRap extruder drive that is compatible with the Darwin quickfit clamp system and the Ponoko lasercut kit. It will take either 16mm PTFE or heatsink based heaters. It is designed to be made with no lathing or machine tooling. An opto sensor may or may not be fitted to regulate rotation speed - I found that this was definitely required with an all-metal heater assembly. If you develop software to do that, we'd love to see it!
The design uses a 50mm M5 drive screw which can be cut from an M5 bolt. Coupling is by an M5 grub screw lock-nutted to the top of the drive screw; a 2.5mm hex key replaces the Tamiya output shaft and docks with said grub. Filing the point off the end of the grub screw will make it easier to fit.
You'll need an assortment of M3 nuts, bots & washers to assemble it. Put springs under the 4 screws holding the filament and screw holders together so that compression is maintained as per the original RepRap screw extruder on the RepRap wiki.
There is a cavity in the screw holder to take another locknut and two washers that are used as a thrust bearing. The drive screw is also supported near the point of contact with the filament by half an M5 nut which has been drilled out to 5mm. With luck, anyone should be able to source these components worldwide.