The Y piece, catastrophic converter is available from RockAuto, and the muffler, surprisingly, available on eBay.

The piece between them, I guess called the “Resonator “ costs $180 from Autozone!   Is this my only option?;

A later model part from a junk yard might be the same size, but I don't know. It should be the same length and diameter in order to do the same job.

If you need one and can't find it, make one.

The resonator is just an "empty" chamber that helps to remove the high frequency sounds from the exhaust before going to the muffler. If you use a pipe to bypass it, you may not like the sound of the exhaust, or maybe you will. 

Measure the body length and diameter of your resonator. Get a piece of exhaust pipe the same diameter and cut to length. Most auto parts stores have on hand 18" lengths of exhaust pipe at least up to 3" dia. and adapters to bring it down to your Brats exhaust pipe size. Install pipe adapters on each end of the big pipe with the ID of the small ends of the adaptors to match the OD size of your exhaust so they will go over the out side of the exhaust pipe. I would have the unit welded for less chance of leaks. Some guys spray paint the welds with high temp paint to help control rust. The odor will go away in a short time. Cut the old resonator off, use two clamps and your done.

I've been running my Brat without a resonator for over 20 years. Not a problem. Unless you are doing a full on resto forget it and replace it with pipe.

13 hours ago, mkoch said:

The Y piece, catastrophic converter is available from RockAuto, and the muffler, surprisingly, available on eBay.

The piece between them, I guess called the “Resonator “ costs $180 from Autozone!   Is this my only option?;

Look for an online discount code and buy the one from AZ. I've done that at Advance Auto Parts about 100 times, though they have cut back on the real good ones in the past year. 

Search for the autozone part number - someone is supplying them and likely they're available somewhere else.  Unless it's just one of those listings that you'd eventually click on only to find out it's no longer available. 

Previous suggestions are really good as well.