I vaguely recall something about the cathars being a secret organization of pagans & gnostics. I know otto rahn's book lucifer's court recounts him following in the footsteps of cathars in search of the mythical grail. Have you tried searching the library about it?
No idea what you read about the fleur de lis. It's just a flower, it can mean anything, just like the fish or any other natural symbol. Most just think of france when they see it.