alamark, aside from getting these guys as hitchikers, i have never seen them for offer anywhere else. thats a good question. i really dont know what to tell you except try some tonga or fiji live rock, as thats where mine came from.
coral, the white band sounds almost exactly like the shield limpet, however they are algae grazers, and do not eat hard corals. one way to tell for sure. if it is a limpet, the white thin gyou are seeing is a shell you might try poking it to see of its hard. if it is its prob the limpet and i would nt worry about it, however if its not, it might be a predatory worm, or possibly a nudi!
good luck
jon