It doesn't have to be done by a single organizaiton; but it COULD be done by a voluntary association known as a government. This type of government would have the credibility backed by a large plurality of the people, and that would give it weight.
My point is that the government doesn't have to use force to be a monopoly on the use of force. It would simply be the largest organization in the area, created and maintained to ensure justice and national defense. The biggest fear that people have, regarding a society with no government, is that they wouldn't feel secure in their persons, places, and effects. So, let them organize, voluntarily, to solve those fears. Let's support a voluntary minarchy, with no more power than any other group, and we'll solve the dilema facing almost all people who disagree with the voluntarist position.
We need to not only tolerate, but push this idea. The Texas provisional government in 1836, was just such an organization; yet they raised an army and defeated Santa Ana in their war for independence. The principled minarchy has teeth, and has a monopoly on the use of force, simply because it would be composed of the largest number of people.