I've seen them at Novare and Bier Cellar lists Madamin on their website. So they are definitely available in Maine, even if not widely stocked.
I think I've had some samples once, but sours generally aren't my thing and they're kinda pricey for a style I don't prefer....
I believe I've seen both Madamin and D'uva at bier cellar. I've also seen them on draft at Ebenezers and Novare Res.