If you’re looking to buy a business on Main Street in coastal Maine, you have plenty of options. Many are historic buildings that include ground-floor businesses with residences above or behind them, often overlooking the waterfronts that were once economic drivers in larger downtowns. Some have been on the market for months. Entering the county in Bucksport, the former home of the Bucksport Enterprise newspaper at 105 Main St., overlooking the …