"...to get ghost ring sights put on..." Shouldn't be any trouble at all. 590's are drilled and tapped out of the factory. Some of 'em come with ghost ring sights. Not with a bead though. You may want to think about buying a rifle sighted barrel and putting on the ghost sight. Or buying a Mossberg Ghost Ring sight kit. Runs $69.46US from Mossberg.
Epp's is a Mossberg dealer. Start there.