Same with the Titan class items. Either it's a bug, a rare drop, or more likely we're gonna be getting another set of tonics during act two that will reward us with the class items, among other things. On the latter note, I did end up getting an exotic tonic at some point during tonic crafting. It's for ascendant shards, even though I don't have the recipe unlocked for that. So that leaves me to believe class items will be getting their own tonic in the next 5-6 weeks when act 2 begins.