> the stuff that makes working reactors is the most difficult part of making a working weapons
I'm unaware of this to be true. Civilian reactors are hardly-at-all-enirched uranium reactors. Creating highly enriched uranium or plutonium are completely different processes.
You need more centrifuges, several times more, but not orders of magnitude more.
And you need nuclear reactors to make plutonium. The weapons you can make with plutonium are qualitatively different from the ones you can make with uranium.
Enrichment requires feed stock, and active reactor fuel is much higher in fissionable isotopes than the uranium with which it was fed originally. The U238 naturally breeds up into stable-ish U/Th/Pu isotopes which you can totally turn into a bomb.
Obviously there are such things as "breeder reactors" that are deliberately designed for this. But there's really no such thing as a can't-be-used-for-bombs reactor.
If you're going for the enriched uranium route to a bomb, nobody is going to start with used nuclear fuel, because dealing with the highly radioactive spent fuel is such a huge PITA.
If you're going for the U233 (from Th) or Pu route, yes then you need a reactor and spent fuel reprocessing. But not enrichment of spent fuel.
That "nobody" is misapplied. Certainly it applies to existing nuclear powers, but that's not the demographic in question.
Not everyone has a U mine or pre-existing bomb industry. The question is whether or not having a reactor makes producing bombs easier or not, and clearly the answer is "yes", bomb-making is easier (yet, sure, still a "PITA") if you have a reactor core handy to start with.
"Creating highly enriched uranium or plutonium are completely different processes."
Not an expert, but isn't all you basically need to do is running the centrifuges a bit longer?
Breeding plutonium is a different process than enriching uranium, sure, but with enough enriched uran you will have a nuclear bomb.
And a dirty bomb is bad enough and simple to construct as well.