...where and how might it be accomplished?
I've got a personal design project (downhill mountain bike with a 6 speed gearbox that can use a standard Sram trigger shifter, for anyone interested) and while gearbox bikes have been done and done and done and done over, they all require either a grip shifter with two cables, and I don't believe any of them use the shift barrel setup like a motorcycle sequential box does. I've got a feeling that by adding a pulley of a specific size with a return spring (set to return the gearbox to the highest gear if there's no cable resisting it), getting the cable pull to match up with the shifter, you could use an off-the-shelf shifter and have a nice, compact gearbox mounted way down for a crazy low CG.
the biggest snag with this design project is I really don't understand how a bike sequential gearbox works, so I can't even begin to draw one up, and it's a lot easier for me to understand something if I can hold it in my hands, shift it by hand to see what happens, etc. anyone know where I can pick up a used motorcycle gearbox for relatively cheap? preferably non-unit (don't want an engine to futz around with because then I'll be tempted to stick it into something and hoon around 
)
thanks in advance
