We always bought it from Bamboo and Rattan Works out on the east coast. If you tell them you need it for kids bows, they know what to do.
I once bought a couple of full length poles to test the longer bow theory. I was going to show up at MOJam with a rattan warbow. Problem was, I got it from another supplier and it was bruised all over the place. With rattan, bruise = instant hinge. I never ordered more to try it out again. If I did, I'd get it from the aforementioned BRW.