To keep construction simple and convenient I've found couple of easily sourced items which can be easily adapted to serve as the main connectors.
There is also a tips and techniques section which I'd recommend reading before beginning construction especially if you haven't done metalworking previously. I do emphasise though that the making is really simple and that the only care that needs to be taken is to be neat when gluing and to take care that the piston slides very freely in the barrel.
A parts and tools list is below. Clicking on the links on the left will bring you to a supplier for the part or tool whilst clicking on the right will give the part information.
These suppliers are only listed as a matter of convenience and we make no recommendation as to suitability of part, tool or supplier!