If you're just looking for a Dual-exhaust look with a little bit of rumble, finding a stock BRZ/FRS exhaust would be a great way to go. Look on a BRZ forum or local listings, as they shouldn't be too difficult to find.
The one that I found was at Russ' Garage
, an awesome local Subaru shop. We were working on my exhaust setup and he told me about an FRS they had just put a Perrin Exhaust on. They still had the stock FRS exhaust sitting in the shop, which is when we compared it to my stock Impreza exhaust.
For those who haven't looked already, the 5-Door Impreza exhaust attaches to only 3 of the 4 hangers mounted on the underside of the car. The BRZ/FRS exhaust can fit onto those 4 hangers without any modification to the car or the muffler.