It should be part of getting new skillbooks or changing one type of skillbook into another in Tsunade NPC. But we're still missing those parts of Tsunade NPC. We got only bare minimum of her unlocked at this time. But somehow we're sold items (like said skill page) about those parts? I can't see what's the logic behind that. And I doubt I'm the only one. We'll just have to wait for rest of her to be unlocked it seems...