An excellent effort, thanks a lot!
Thus passes the glory of the world! Well, nothing is forever. There are not very many "critters" left in the world. Built end of the 50-ties to the end of the 1960-ties. Most of them are scrapped, I think that is better instead of having them to rust on a siding!
Only a few are preserved! I Britain there are three. No one in original condition. One location is this place
https://traincabs.co.uk/the-cabs/ which to me is a peculiar place for saving (parts) rolling stock. Further down on that page you find a Neptune 50002 arriving to that location.
My search continues!