Custom dual exhaust

I have a 2004 buick rainier and I want to put a dual exhaust system on it. It is dual until after the catylitic converters, then it comes together with a y-pipe and has the muffler then the resonator. I want to put a custom dual exhaust system on it and my plan is to go from the existing cat-cons back. I'm afraid if I use just one muffler on each side it might be too loud, and I don't know where you can get new resonators. Any ideas?