There are no operable Big Boys and no plans to return any to running condition.
4004: Holliday Park, Cheyenne, Wyoming
4005: Forney Transportation Museum, Denver, Colorado
4006: Museum of Transportation, St. Louis, Missouri
4012: Steamtown National Historic Site, Scranton, Pennsylvania
4014: Railway and Locomotive Historical Society, Southern California Chapter, Fairplex, Pomona, California 3
4017: National Railroad Museum, Green Bay, Wisconsin
4018: Museum of the American Railroad, Dallas, Texas
4023: Kenefick Park, Omaha, Nebraska
http://en.wikipedia.org/wiki/Union_Pacific_Big_BoyMore powerful and slightly less weight were the 2-6-6-6 Alleghenys.
The Green Bay museum is worth the visit, if you can.