Ahh job half sorted. I took one of the old shafts and cut the thread off one end.
This took a bit of expertmentation but finally settled on a washer from under the cylinder head nut. It is the right diameter and hard enough.
So drop it through the bearing to sit on the pin that is held just below the bearing. Then push the washer under the bearing lip and drive the pin against the washer pushing the bearing out.
The minor bummer is that the washer does not fit through the bearing in the other arm.