A SAND source has reported that a new site for the Harborlights outdoor concert venue is being considered by its owners, Don Law Productions, along the South Boston waterfront on Massport property. The site is a parcel at the water's edge along Northern Avenue, immediately east of Jimmy's Harborside restaurant. The new Harborlights site would host approximately the same capacity of 4-5 thousand attendees, but is expected to have a larger footprint than the older venue on Fan Pier.