Recently, American antiques expert Leigh Keno, of "Antiques Roadshow" fame, has been making many housecalls looking for objects for his newest venture — the inaugural auction of Keno Auctions, to be held at the Marriott Stamford (CT.) on May 1 and 2. He's already amassed an impressive sale including William Matthew Prior paintings, among them his only known self-portrait, dated 1825; a Childe Hassam watercolor; Paul Revere silver; an Iroquois ladle; Ralph Cahoon folk art; and a variety of spatterware, scrimshaw and redware. Not to mention important American furniture.