As for GP-30's in Museums here's a few I've been able to find
B&O 6944 B&O Railroad Museum, Baltimore, MD
Cotton Belt 5006 Arkansas Railroad Museum, Pine Bluff, AR
D&RGW 3011 Colorado Railroad Museum, Golden, CO
L&N 1030 Southern Appalachia Railway Museum, Oak Ridge, TN
NKP 900 NKP & Mad River Railroad Museum, Bellevue, OH.
Pennsylvania RR 2233 RR Museum of Pennsylvania, Strasburg, PA
Reading 5507 Western Maryland Scenic Railroad
Reading 5513 Reading Company Technical & Historical Society Temple, PA
Soo Line 700 Lake Superior Railroad Museum
Soo Line 703 Colfax Railroad Museum , Colfax, WI
Soo Line 714 National Railroad Museum, Green Bay, WI
Southern 2594 Southeastern Railway Museum, Duluth, GA
Southern 2601 North Carolina Railroad Museum, Spencer, NC
UP 844 Nevada State Railroad Museum, Boulder, Nev
UP 849 Western Pacific Railroad Museum, Portola, CA