Hi, finally I found it! The instrument you're asking for is called KAYAMBA, from Kenia, Tanzania and Madagascar, the other names are kiyamba, caiambe, kavia, kayambe', kayanm.
It is normally 3-4 cm high and measurements from 18x24 cm to 45x60 cm. Inside it is divided into two parts and is filled with beans, oyster shells and little stones. It is played as an afuche', african shaker and chocalho are played.
It is available from Afroton (frankfurt-Germany) or in every ethnic shop(here in Europe). If you want to know more and receive a photograph with this instrument opened (for inside seeing), send me Your email so I send You the material. Nice to help You, Fabrizio.
fabriperc@libero.it