Britney Spears sought professional help far outside the showbiz spotlight ... 'cause TMZ has learned she hunkered down -- briefly, anyway -- in a small, picturesque New England town. Sources close to Britney tell TMZ, the pop star received treatment at Borden Cottage in Camden, Maine ... a quiet, rural facility where we're told she received dual diagnosis care for both substance abuse and mental health services, following her recent DUI arrest . We're told the super private center sits on a 14-