NEW YORK (Reuters) - Goldman Sachs Group is looking to raise up to $600 million from its wealthy customers for a publicly traded credit fund that will provide loans to mid-sized companies - believed to be the first fund of its kind for the Wall Street bank. The new fund, in which Goldman could invest another $150 million of its own money, is being structured as a business development company, an investment vehicle that is specifically exempt from the so-called Volcker Rule that puts limits on some activities by Wall Street firms. ...