With many restrictions.

Not really. You can buy it on Amazon.

Now, enriched uranium is a whole different story.

Yeah, but don't buy more than 7 kg.

Up to a ton of ore I believe, as long as you don’t refine it. The rules are a bit inconsistent.

As long as you don’t hurt anyone with it, or try to blackmail the US with it.

[https://www.law.cornell.edu/uscode/text/18/831]

The 7kg limit is apparently a ‘depleted’ (aka refined/filtered) thing - https://www.nrc.gov/reading-rm/doc-collections/cfr/part040/p...

But commonly misquoted.

7kg is a pretty large quantity.

It can be up to 150lbs a year if extracted from drinking water (!!).