Also, you don't HAVE to have the special thyristors (I've forgotten the proper name) in a nuclear bomb - there are other ways of initiating the explosion timing. And even if you did need them, thy could be smuggled from China or elsewhere
Except the bomb would then be the size of small car, and undeployable except by low-level C-130, overland, or by ship - ie would never get anywhere near a strategically useful target. And no, you are utterly wrong that they could be smuggled from China or indeed anywhere else - substantial diplomatic and intelligence resources are devoted to preventing that possibility.
I'm looking forward to reading the imminent UN report. Interesting to read today that Russia (having no doubt already read the report) are already strongly vetoeing a pre-emptive attack.