Delta Air Lines said it received final approval from the South Korean government for service from Atlanta to Seoul. The carrier plans three round-trip flights a week beginning Dec. 15 . . . Chrysler Corp. Chairman Lee Iacocca has been granted a divorce in Pontiac, Mich., from his 37-year-old wife of 18 months . . . Chalco Industries of Gardena, an aerospace and electronic firm, will buy privately held Downey-based Olympic Fastening System, paying for the acquisition with 2,453,712 new common shares. Chalco posted sales of $5.25 million in fiscal 1987 and lost $114,000 . . . Toronto Sun Publishing Co. has completed its sale of the Houston Post to MediaNews Group of Dallas for $100 million in cash plus a $50-million five-year note.