ByTim Stevens Looking to buy or sell a small- or medium-sized business? Services and resources provided by the U.S. Business Exchange, Santa Monica, Calif., can help. Using a search engine and financial, product, and market criteria, users can locate one of more than 6,000 businesses for sale at the listing exchange. A resource center provides industry-specific merger and acquisition news and information, plus tools for establishing a valuation range for an enterprise. Links also are provided to additional services including merger-and-acquisition attorneys and lenders, and a forms center offers downloadable documents required in buying or selling a business.