My dealership was just as ignorant, I ended up buying the Invidia cat back system.
Sure, they'll sell tuner parts for the scions, but ask for tuner parts for a real Performance car, and they get all stupid on you.
Just order it online, or call the other local toyota dealerships and request the info, you're sure to find a hook up. and yes, the TRD
exhaust fits ALL 7th gen model years, so if they don't have it for your model year, ask about the earlier model years too.