"The only stuff that might be an issue is the "secret sauce" and even there it's a classic make vs. buy decision."
What are you talking about? That's the WHOLE POINT.
Anyone with enough fissionable material ... and able to smack it together fast enough ... will produce a fission "bomb".
WHERE are you going to get that amount of fissionable material?
"The reason for the concern is more the latter, how much confidence do you have that all the former Soviets are really to be trusted not to have lost some fissionable materials?"
There are many old master paintings that have been lost. We know this.
Now, if someone comes up to you offering to sell you an original, never before known, Renoir ... Just because something is not accounted for does NOT mean that it is available to you for purchase.
"Point is, in the modern world you don't have to duplicate anything that's been done widely enough."
And by "widely enough" you mean "you don't have to duplicate" it.
Nice circular logic there.
"Where did India and Pakistan get their fissionable materials?"
ZOMG!!! You've found the flaw in my position!!!
Duh, they have uranium mines in their countries. Their countries are situated on top of uranium deposits. They dig the uranium up.
As was stated earlier in this thread, that requires the resources of a NATION.
And it requires a LOT of uranium.
"How confident can we be that they, and everybody else possessing significant quantities of fissionables, can be trusted to keep them under control, at all times, forever?"
Ummmm, since the half-life of those materials is far, Far, FAR less than "forever", the answer is 100% positive. The materials will be inert long before "forever" arrives.
"Without a satisfactory answer to those questions, ..."
Again, because you do not accept the answers, the answers are not "satisfactory" to you. Nice circular logic.
You watch too much TV.
Terrorists with nukes are not something to be concerned about. They cost too much. They require too much expertise. They require too much technology. They require a NATION to build / maintain / support.