I'm pleased to report that no one has ever seen a live round in any museum; nor are they ever likely to. A better description would be a former operational round. There are two of those that I'm aware of. One is at the Boscombe Down Aviation Collection, and the other is in the Historical Collection at the Atomic Weapons Establishment, Aldermaston. Sadly, that museum is inside the security perimeter at AWE and not open to the public; although access is possible by special invitation.