Ownership of Artifacts Before you and I ever get a chance to acquire a lunar artifact it has to have been relinquished by its original owner. Of course, that's an obvious statement but with lunar artifacts it is not such a simple matter. NASA transfers ownership of all artifacts it no longer has use of to the Smithsonian. My understanding as this applies to lunar artifacts is that this relates to all hardware which was originally intended for return to Earth. Items not manifested for the trip home, such as anything the astronauts decided to salvage, is not the property of the Smithsonian and remains with the astronaut that retrieved it.
Items flown in the astronauts' personal PPKs are also their property.
Should you decide to acquire a lunar artifact, than I would suggest the optimum method is directly from an astronaut. If buying direct, you have the opportunity to insure the documented history and provenance is exactly as it should be and this alone is worth the efforts. There is also something almost magical about acquiring something direct from the person who flew it. The reality though, is this isn't always possible so one must seek opportunities within the space memorabilia marketplace. My own experiences have lead me to the belief that auction houses are not the best place to buy artifacts.