It's probably rare that somebody walks into a Denny's with a moon rock in her purse, but that may have happened in California recently.
According to the Los Angeles Times, two men met with a woman in a Denny's restaurant in Lake Elsinore, California, and agreed to buy a moon rock from her for $1.7 million. In fact, the meeting was a sting operation that concluded a lengthy investigation by NASA and local police. When the woman produced the alleged moon rock, NASA agents "swooped in" and took custody of the item.
Apparently it was indeed a rock, but where it came from isn't clear yet. "It's possible this is a moon rock," said a NASA inspector general, "but it has to be tested first." People do occasionally attempt to sell actual moon rocks, but it is more common for someone to offer a bogus moon rock in an attempt to scam someone. NASA is not yet sure what the case is here.
The Times story states that "[m]oon rocks are classified as national treasures and owning them is illegal," which is half true. They are national treasures, but so far as I can tell it's not illegal to own one. As I have written before, it's just that moon rocks are so difficult to come by (assuming you aren't on the Moon) that any private citizen who's got one probably stole it or got it from someone who did. Possession isn't illegal, but stealing is.
This is likely why the woman wasn't arrested, as the report also points out. In an SF Chronicle report, a former NASA investigator stated that the woman could be charged with theft if the rock turns out to be real, or with fraud if it isn't. He didn't say anything about being charged with possession of a controlled lunar substance.
The only original source of moon rocks is the Moon, and they are lying around all over the place up there but it's much more difficult to get one on Earth. There are lunar meteorites, which get knocked off the Moon by impacts and end up down here, but those are ultra-rare. Going up to get your own is hard enough that only the Apollo missions and a few Soviet probes have ever come back with any. Apollo brought back about 840 pounds, most of which is still in NASA custody. Some are in museums, and scientists have some.
But the U.S. did give away moon-rock fragments (on plaques) to all U.S. states and most foreign countries in the 1970s, as a gesture of goodwill, and lots of those have gone missing, in addition to some that were stolen from NASA a few years ago. One of these turns up every now and then, and NASA's moon rock squad is usually not far behind.
For more on this topic, including the story of the one published legal opinion involving moon-rock ownership, see "United States v. One Moon Rock."