Was Itachi Jiraiya's source in Akatsuki?
This is a really good question and its very possible, but you also severely underestimate jiraiya's abilities. As the Toad Sage he could literally have toads all around the 5 Great Nations listening for information for him, and the reason i have for this is he can summon almost any toad from Mt. Myuboku. And use normal toads to aid him in infiltration tactics. I mean look at the way he infiltrated the Hidden Rain Village right before his confrontation with Pain. He used a normal frog, not even a ninja frog, a normal frog. So despite the doubts you have he could have toads around the 5 great nations listening for information on the Akasuki. Like i said it is very possible for Itachi to have been the spy for Jiraiya, but at the same time i do feel you underestimate Jiraiya.