None of the major defense contractors (new or old) would be interested in doing this unless they could greatly pad out their numbers. There's a lot more money (see F-35) in building out a new system and landing the huge maintenance contract for the first 10+ years associated with it. A B-52 clone would be financially great for USAF if it could be built at an appropriate price since they have the maintenance capability for that airframe already, but no one would sell them one at the right price.