When I got a matchlock teppo I started looking up Japanese accoutrements. They used speed loaders made of wood, including bamboo. They were just cylinders the size of a powder measure with a plug in one end. Part of the shooter's equipment was a rectangular belly box to hold them.
I have also found some photos of Japanese powder flasks, but they seemed to be turned of some wood other than bamboo. They were canteen shaped, like two shallow wooden bowls put together, maybe 6-8" in diameter.