Mostly from Palau in the ancient times. Many them were brought from islands as far as New Guinea. The value of the stones depends on the size, history and how shiny they are. It is difficult to obtain them which is why the value is kept high.
The piece are owned by different people. Often they change ownership due to marriage, transfers of land or compensation. Although, it is unnecessary to move them as this can be difficult due to the size and weight of some of them.