Yes I know this is an old thread. I only get on here about once or twice a year... but this may help someone looking for a complete solution.

My 2000 Xterra, bought new (build date of May 1999), currently has 208,523 miles on it and still has the factory exhaust from the engine to the point the muffler bolts on! I have went through two mufflers and one O2 sensor in all that time. I am about to do the third muffler. I am going to buy just the muffler, tail pipe and clamps from these guys: https://www.carid.com/replacement-exhaust-kits.html

They do carry COMPLETE kits including the cats. Hope you have a cutting torch as getting exhaust bolts off is not going to happen!