There are of course other ways to legitimize property such as the NAP.
The NAP only has legitimacy when given the force of law. Before that can happen it must be carefully defined for you seem to have admitted that even it has limits and requires a nuanced interpretation. The process of giving a principle legitimacy is called "lawmaking". To make a law you must have a group empowered to make those laws. It is absolutely unreasonable to expect absolute adherence to those laws without an enforcement mechanism.......and so it goes.
I think you have insufficiently argued why gouvernement is the only possible source of legitimazing property.
What does "legitimizing property" mean anyway? Are you imbuing property with rights or are you giving rights to the individual who possesses it? A rock has no rights so the issue is what my rights as the possessor of that rock are. We know that I shall not own that rock forever. So there are limits on my possession of the rock.
We see an interesting example of that right now. ISIS possesses a part of the Middle East. They claim that they legitimately possess it. So this group decides to destroy ancient monuments and works of art. They are destroying the heritage of the entire world. But if property rights reign supreme and the legitimacy of those rights begin with possession, what they are doing is just fine. But we both know that it is not. It would be fatuous to argue that the are aggressing against the owners of this property unless you first conclude that there are rightful owners and that those owners are so large and diverse a group that this group transcends international borders. Now you are in the realm of international law. Who makes that?
What if the property you are attempting to imbue with rights is a book? I possess the book. I purchased it from the author who, created it for a particular purpose. Do I therefor own the right to reproduce this book for sale to others? Many ANCAPS, mostly young, so want to pirate video games, movies and music that they draw a line at intellectual property. Are you one of those? do you maintain that the rights to my song end when I put it out there for sale? If this is true of a drug, the result will instantly end research into new drugs which, if we as a group want to further medical research, means that we must fund, through some mechanism this research. But you would eliminate government in that process.
Suppose I invent a new process to purify sea water for human use. Should I have the right to exploit that process for profit? Who then owns the water I produce? Who owned it before? Are we to conclude that 'you' own the right to sell the land on which I build my plant to me for profit, the electric company owns the electrons and the wires that go to my plant and may profit from them, and the manufacturers of the equipment from which my plant is made belongs to them so they all may profit from them yet the decades of research and hard work that I invested in developing the process has no value at all other than to be present at the starting line? And that once my research is out there, anyone may exploit it at will because it is not "property"? And who owns the water from the ocean? May any person claiming inconvenience force millions to be without water because we have imbued their property with inalienable rights?
So do you maintain that the absolutely mundane possession, a book, has "rights" but the extraordinary ability to order the words within has no value at all?
Now you have endlessly maintained that we have not presented arguments counter to yours. We have, of course. I have asked you many questions, above. In a debate, it is customary for you to answer them. I do not expect you to do that. You wish to argue simply at some macro level but the devil is in the details as they say. Have at it. No more claims we have not laid out an argument. Get to work and defend your position.