Thanks to all of you kind Train folks for responding. We have found a Big Boy from a forum member in Pennsylvania and are in the process of getting shipping etc sorted out.
What I learned is that MTH Railking, Lionel LionMaster and Kline all made a version to run on 031 which still surprises me. The Lionel and MTH versions are larger while the K-line is basically shrunk down, but still a beautiful engine. So if you have a layout with tighter curves , you can still have a Big Boy. Can’t wait to try it out!