Where can I buy a 'water disc' for ball valve

Can anyone tell me where I can buy a product called a 'water disc' which is attached to a ballvalve and acts as a damper to stop the ballvalve arm from osolating and preventing water hammer in the pipework as the
cistern completes its fill. Cant get one anywhere. Used to be able to purchase it from S.E. Borrows of Waterlooville Hampshire, but they have ceased trading, and new company no longer stock this item, or know anything about it.

Readers digest suggest hanging a little bucket on the arm to stop the bouncing

I've got one somewhere I bought from a local merchant, if you REALLY want one! Try a square of polystyrene with a 2"hole in it. Float on the water with the ball sitting on the hole. The float irons out the waves.

Or suspend a square of plastic under the ball about 3 inches square.

Alan