I photographed these North American X-15 examples at the National Air & Space Museum in Washington DC, and at the Evergreen Aviation Museum in Oregon.
North American X-15A-2 56-6671
NMoUSAF 2018
North American X-15A-1 56-6670
Smithsonian NASM 2015
North American X-15 mockup
Evergreen Aviation Museum 2015
painted as 56-6672