South Korean companies' equity and debt sales tumbled 27 percent on-month in May due mainly to a plunge in stock issuance, government data showed Wednesday.Local companies raised 14.5 trillion won ($12.7 billion) by selling stocks and bonds last month, compared with 19.8 trillion won in April, according to the data from the Financial Supervisory Service. Stock sales, including three initial public offerings, reached some 90 billion won, down a whopping 96.8 percent from the prior month."Sto