Hello SIPAUL
Try ebay under Norton , then vintage, there is a three brush one going for sale £40 or so.
Make shure it has the correct rotation for the dynamo, do a drawing working out the rotaton from the oil pump side.
The third brush on the dynamo will only work with the correct rotation. The cut out is located in the cover on the end make sure that is there as well.
Remember it is the dynamo's rotation that is important not the mag, as the mag can be made to work in either direction.
I am doing a 1932 model 50 so we have been there, good luck Charles.
