Lost Pindle

Have you tried contacting PistonBikes to see of they will sell you one?
I have no idea if it is a press fit, but just by looking at where it is and what it has to do, I will venture to guess that it is a hardened pin. If you have to make one, I recommend using the smooth shank portion of a drill bit cut down to appropriate length.
Here's a link to the page referenced if anyone else can help.
part #21.
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that little short pin?slide your parts togeather and see if goes through the collar and if the spring dosn't hold it in place,I think the spring does,the spring pushes it(the collar) to slide the mandrel the flower (clutch fine adjust) nut is on to pull the clutch plate against the pucks,,,I do not think it is a press fit but it may be hardened as a dril bit shaft would be,and just the right length to fit securly in both holes of the collar the spring pushes against

its not a press fit. it slides in place with everything apart. My guess is if you can find a small screwdriver that will fit the hole cut the screwdriver shaft to fit or use some coldrolled steel
rod probably even hot rolled steel will work.
a dremel with a cut off wheel works good for cutting the metal.