The shaft is not available as a separate part. The usual cause will be calcium built up and locked the shaft to the drive unit. The two options are, try to repair it, or replace the motor block 6055.100. To repair it, you will need to salvage the shaft, it may need to be pulled from the drive unit with pliers if it is really stuck, be careful to not mar any more than the end of the shaft that will be pressed in the pump. Clean it well and try pressing it into the socket in the pump, if it is still fairly tight, you can probably save it. I would drill the shaft socket a little deeper, this should be done carefully and I would use a bit that is a bit more than half the diameter of the shaft. Add a drop of super glue to the end of the shaft and use a press or gentle even hits with a hammer and a punch to seat the shaft, if the shaft is bent it will be ruined so this has to be done carefully. If the shaft fit is so loose it wobbles, it cannot be saved.