HONG KONG, Aug 20 (Reuters) – Chinese regulators are considering pressing data-rich companies to hand over management and supervision of their data to third-party firms if they want U.S. stock listings, sources said, as part of Beijing's unprecedented scrutiny of private sector firms. The regulators believe bringing in third-party information security firms, ideally state-backed, to manage and monitor IPO hopefuls' data could effectively limit their ability to transfer Chinese onshore data overseas, one of the people said. That would help ease Beijing's growing concerns that a foreign listing might force such Chinese companies to hand over some of their data…