I’m new to unicycling so I have no knowledge about ancient stuff, but what exactly are you looking for? I might have some alternative source (bikes) where you might be able to find a solution.
- Why is the bearing size relevant for the cranks?
Or is it the width of the bearings that is different as well?
- is it square tapered or isis?
Onza is a bike trial brand, so it’s very well possible that you could find matching cranks in a bike trial shop.
These are from Comas, but square tapered and 130mm:
I’m not expecting it to be the right cranks, but it might provide you with alternative solutions