FRANKFURT (Reuters) – The owners of classified ad firm will announce plans in October to list part of their holdings in an initial public offering in Germany, two sources familiar with the transaction said. According to the sources, the owners plan to float about 25 percent of Scout24 shares, with a potential value of 500-700 million euros ($648-907 million). The IPO comes only months after private equity firm Hellman & Friedman and Blackstone closed a deal to acquire a 70 percent stake in Scout24 from Deutsche Telekom for about 1. …