My sunbeam mixmaster is stuck on one speed - fast!

Question

I have a sunbeam model A12 (approx 1964) and it has never missed a beat, has had regular services and has now become stuck on the highest speed.

There are very few electroncs palces around and no on seems tobe able to help me as I ahev been told that it needs a new speed ball and they can't get th eparts any more.

Can you help? Where can I get a speed ball for this model.