SG Cowen is on the prowl for third-party money for its internally managed convertible arbitrage hedge fund, currently seeded only by SG capital. The fund, which has been running for several years, has achieved strong returns and the firm feels this track record allows it to solicit outside money, explained one official. The fund's assets under management could not be determined by press time. Robert Marx, who heads up the fund, was traveling and could not be reached and Jean Calleja, spokesman in New York, declined comment.