Anybody know anything about the marantz model 15?

One of the green bulbs are burnt out. Where does a marantz romantic find a Dialco 507 3909? I also have a repair manual for this, but no parts list or exploded views. The amp works and looks like new, typical it seems for the older units. If I should encounter problems, does anybody know where I could get servive for something this old? I would be willing to ship. Thanks, everybody!