I did manage to find a used swingarm bolt from a Kawasaki er6.
A spacer is needed on the left side. Hmm my bicycle saddle pole could be the right diameter.
Inner diameter: 24mm (Should be 20mm)
Outer diameter: 29mm (Should be 25mm)
Wall thickness: 2.5mm
Cut the pipe to the correct length and sawed a slit at one side.
Some work with the polygrip and a hose clamp and it now has an inner diameter at 20mm and a outer diameter at 25mm.
A perfect fit!
The threaded part need to be extended and the axle cut to the proper length.
That will have to wait until I can get hold of the correct die for the threads.