Napa
I work at NAPA about 5 minutes away from Enterprise Engine. The guy who EEP recommends for all exhaust work on the Dodges comes in to NAPA all the time. He gets everything he needs to do stacks or any other exhaust for that matter at our store. Anybody else who wants to do a larger exhaust usually goes to NAPA to get it. On average, we probably sell stacks and all the piping to 4 or 5 people. It seems like every day there is a new guy who is putting stacks on his truck. We kind of used my truck as a show truck for different exhausts (I've had 5 different exhaust setups on my truck in 10 months, including dual 5" miter cut stacks). It should only take you about 2-3 hours at most to install stacks- start to finish, and shouldn't be any more than about $550. Our store keeps all the piping and a variety of stacks in stock because we turn them over so quickly, but any NAPA store can get them in a few days. Just my . 02.
John