According to H. Pearce Commercial Real Estate, Peter Harding purchased a 6,500 s/f building at 210 South Main St. Harding acquired the property in the name of Mackey III, LLC, one of the various interests of Harding Development Group, and plans to totally renovate the building.   Harding Development Group is completing their Liberty Sq. project on the corner of Main and Liberty Sts. and anticipates starting work on the new South Main Professional Center in early October. Virginia Vinci and Neil Riley of H. Pearce Commercial represented the seller, Sebastiano Santostefano and Tom Coughlin of Management Services, Inc. represented the buyer.