A Korean-American businessman accused of trying to buy deadly nerve gas boasted of high-ranking contacts with the Chinese, Yugoslav and South Korean militaries, a prosecutor said at a bail hearing in Newark, N.J. U.S. Magistrate Ronald Hedges set bail at $2 million for Juwhan Yun, 49, of Short Hills, N.J., imposed strict travel restrictions and forbade overseas contacts. Assistant U.S. Atty. Anne Singer said Yun also sought to buy sophisticated automatic grenade launchers during negotiations with a U.S. Customs Service agent posing as an arms dealer. Yun, owner of Komex International Corp., a Summit, N.J., import-export firm, was arrested Thursday after a seven-month undercover investigation by the U.S. Customs Service. He was charged with conspiring to export illegally the nerve gas sarin.