but certainly not hundreds!

No one said there was. Truly rare is something like a Beardmore Tornado of the type used in R.101, only one or two in the world (Science Museum and an engine block at East Fortune, any one know of more?). The insurance on these would be much higher from a museum point of view than a Jumo 004. There are Jumo 004s in every country that has an Me 262, and then some. The UK, the USA, Australia, Czech Republic, Germany, there’s probably a few engines lurking about in Russia, maybe one (some) in France. Probably more out there, I don’t know exactly.

Stampinot, like I said earlier, get the museum you are loaning the engine to, to contact other museums for advice and to avoid headaches later on, make sure you get proper documentation from the museum clearly stating the terms of the loan agreement before you hand the engine over.