Yeah they exist, I just got one last week. I think its a Valedictorian with Arc damage and tracking. The other perks I received on it are junk, think its Vacuum or something and no velocity increase for the other tree. I can put it on if you haven't seen any. I'd prefer to run Hezen vengeance over it, that thing destroys and gets no respect. I'll equip it on my hunter in case anyone wants to see but I hate dropping my trio of Gjellies. I also thought they were unicorns, in fact I haven't gotten a single decent Arc rocket launcher since the DLC for dark below dropped. So I finally have an Arc RL, the only downside is Vally has TERRIBLE velocity. Oh well at least I have an arc launcher in case I need it. I usually just run my Against All Odds field scout mg if I need arc for a burn.