I know that Coleus will be happy to part with some, and Fishytime would give you some as well, just pm them. And yes, you can definately grow it in your sump, just place a simple L.E.D light overhead, and it'll grow like a weed
In order to control growth, just keep the chaeto light on a reverse cycle with your tank lights. Tank lights on during the day, chaeto light during the night. It's what I do, and I dont have to trim my chaeto too often. Good luck
