Experiments show that, on average, 3 out of a 100 small stones will break when used. These have the identical range of throwing stars. After update 8.5 the drop rate of small stones by goblins was lowered and prices became higher.
The easiest way of getting small stones is by hunting apes. Sibangs drop them quite frequently. Earth Elemental also drop nice amounts, but are considerably stronger to defeat. They were once a common drop of Goblins (Even 3 Pieces per kill). The Price has increased dramatically since they are dropped less commonly.