Planted Tank Guru
Join Date: Dec 2002
Location: Portland Orygun
I know that Robert has it at AquaBotanic, not sure of the size. If you check AquaBid you can normally find some large ones for sale there. It's actually very common and I can't think of any on-line seller of aquatic plants that would not have it. The only hard part would be finding the size you want.
The rhizome is the thick root like item that the plant comes from.