Lane, the exhaust consists of a downpipe & catalytic converter, a resonator and a rear box. The first two are an integral unit, as are the last two (from the factory, at least).
If the cat is clogged, put a vacuum gauge on the engine and rev it. Vacuum should fall to 0 from anything between 15-22 at idle.
There are plenty of sources for used exhaust systems, but I don't recommend any of them. A new one is your best bet; the logic here is that the one currently on the car probably lasted 15 years, and a new OEM will give excellent performance for an equal amount of time (probably longer than you'll have the car).
The rattling could be from a rusted heat shield, or -- more likely -- a bad rubber doughnut or figure 8.
best, whit