Ray Man used to sell them as Monkey Drums, or pellet drums, beautiful little talking drums held in each hand, altering the tensions as you shook them.

Is Ray Man still there? (Quick Google search) Yes he is - check Here; doesn't look quite the Aladdin's cave it was back in the early 1980s when it supplied exotic hardware to the entire UK free improvisation & experimental fraternity; I still have gongs & drums I bought 27 years ago... But still worth a look I shouldn't wonder...