[khuey]

Atomic bombs are useful for blowing stuff up (which requires detonating them) or threatening to blow stuff up (which requires other people knowing you possess them). "Laundering" a bomb that remains unknown for 50 years doesn't seem that useful.

[MichaelCollins]

At least one country sees value in being deliberately ambiguous about possessing nuclear weapons.

[RichardHesketh]

Unless it was taken apart by another state for research purposes…

[khuey]

Probably easier to get your hands on some engineering documents than an entire bomb.

[MOARDONGZPLZ]

Seems prima facie easy, but at least in the USA each part is certainly contained within a different special access program, and never the twain shall meet.