I mean if you want to give them some kind of lore, then I would say they go as far back as Asura and Indra maybe? They only know the legend of the Otsutsuki clan, even the founders of Kara only ever knew the legend. However, that'd almost make them a long lasting clan rather than an Akatsuki type organization, wouldn't it? It would be much safer to say that they are a result of the war itself, and the discovery of the origin of shinobi. Ao could have been saved by the current leader before Kara, or a member.