We don't when Jiraiya started to track the Akatsuki. He didn't know any of their names. Only info Jiraiya got was that there was 10 of them and Itachi is among them. Which he probably got from crossing paths with Orochimaru.They aren't Zetsu clones. But if they were is that a good enough reason to justify 10 years of not finding them? Jiraiya found them easily enough and Zetsu was a part of that Organization then.