There used to be one right in ??????? (whatever the LL bean town is). I think it was Coastal Aquatics, Anna ??? I think was the owners name she was a member here. (coastalAnna ? Maybe?)
Oh well that's lots of Maybes but lots -O- clues too
Portland used to have a couple reef stores a few years ago. One on the Airport road, and I think another down off Commercial? I don't quite remember, and that was a couple years ago, so I can't say whether they're still around.
Are you wondering about a particular part of Coastal Maine? South of Portland? Eastport? It's a really big area (with few reef stores).