You may be able to find uranium ore with relative ease, but enrichment is a nation-state level project that is unlikely to escape the notice of the world's intelligence and energy agencies.
> Uranium-235, while occuring in natural uranium to the extent of only 0.71percent, is so fissionable with slow neutrons that a self-sustaining fission chain reaction can be made in a reactor constructed from natural uranium and a suitable moderator, such as heavy water or graphite, alone.
https://fas.org/issues/nonproliferation-counterproliferation...
Also, anyone who can build a Farnsworth Fusor could generate neutrons suitable for enrichment. You are overestimating the difficulty of obtaining and producing dangerous quantities of radioactive materials. This is a convenient falsehood as it breeds a level of comfort in the population, but it is certainly not true.
In any case, you have everything you need for a dirty bomb.
I don't think this is what you meant, though. Why can't [an independent actor] recover Pu-239 from the core of a uranium reactor? I'll admit I don't know a lot about chemical reprocessing, but the proposition here is using a series of highly corrosive and/or explosive chemicals ([fuming] nitric acid, tributyl phosphate, hydrazine) to extract Pu-239 from very radioactive irradiated fuel rods with unknown actinide concentrations. Chemical reagents for this process (e.g. for PUREX, tributyl phosphate) are controlled and monitored by non-proliferation agencies. Chemical re-processing will not separate the Pu-240 from the Pu-239. Pu-239 is unsuitable for a gun-type weapon, as it is so fissile that it will blow itself apart in a partial detonation ("fizzle") before the slug and target are brought together--this means you need an implosion-type ("Fat man") weapon to effectively use Pu-239 as a fuel. A high concentration of Pu-240 exacerbates this problem. A fizzle in a populated area is still very bad, but not bad in a way that couldn't feasibly be produced by conventional explosives and/or chemical weapons much more easily. In order to produce enough Pu-239 to form a weapons core within years instead of decades or centuries (provided extraction is feasible), the independent actor probably is looking at a >1 MW reactor with the cooling towers and infrastructure that surrounds a project of that scale.
It is really only a viable threat for a terrorist organization if that organization has the clandestine support of a nation state.
EDIT: Or otherwise enough financial support, technical expertise, and freedom of activity to engage in serious construction projects and industrial chemistry. The point is that it's not something you can put together in a basement lab.
>is unlikely to escape the notice of the world's intelligence and energy agencies Thats how Iran and Stuxnet came together.
Some history https://www.miningreview.com/uranium/avoiding-covid-fatigue-... https://en.wikipedia.org/wiki/Uranium_mining_in_Namibia#Back...
Teflon as mentioned in the Youtube vid at the beginning also demonstrates another way to enrich uranium. Are those the only two? I think not.