From public “type-ins” at bars to street poets selling personalized, typewritten poems on the spot, typewriters have emerged as popular items with aficionados hunting for them in thrift stores, online auction sites and antique shops. Some buy antique Underwoods to add to a growing collection. Others search for a midcentury Royal Quiet De Luxe — like a model author Ernest Hemingway used — to work on that simmering novel.