Speculation, but I think this hints it...
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They called out to him, the weapons felt his will-the will of the solo.
The will of solo.
Solo weapons are attracted to solo kings
Because Itachi didn't chose the solo life, the solo life chose him.
I doubt he looked for them. They're not objects that he could use without Susano'o after all, if he founded them like normal objects such as a kunai or a shuriken he wouldn't needed Susano'o to wield them. He most likely awakened them along with his Susano'o.
Nope, Orochimaru was looking for them, they existed Itachi ever had Susanoo
Orochimaru pursued a myth regarding those weapons, he most likely thought they were normal objects but manga showed they're made of Susano'o material therefor cannot be wielded without Susano'o. And those myths confirms they existed before Itachi, I never said otherwise.
They called out to him, the weapons felt his will-the will of the solo.
God himself descended from Heavens to give Itachi the weapons he forged for the Solo king.
Than the weapons must have had a physical form beforehand, unless everyone is implying they originate from susanoo? Because Madara was the first Uchiha after Indra to be recorded having susanoo, those myths didn't come from strangers who witnessed other Uchiha with susanoo to awaken them, because that negates the fact of Madara being the first recorded, unless Indra had them, and the folktale spread through generations from his time, otherwise Totsuka and Yata were actual physical weapons, and how they were converted to spiritual susanoo weapons is all speculation.