I read you can get the Nightbarb scan in the first room of Bryyo, but I can never see em... I wanna get em now or else it'll eat at me until I get that scan :(
I think they just fly overhead as you're heading to the door. It's really easy to find them later on. After crossing the ice bridge, the big room there will eventually have them everywhere. Just check back there every so often and they'll be all over the place.
I;ve only seen them in the first room on the FIRST time you get to that room. You have to be pretty quick to scan them there. If you miss no worries because they appear in other places plenty.