I found the resonator on the brand X site Rock Auto. I checked Peachparts and all they have for the exhaust on this car are the gaskets and hangers. But they are the original so you might want to look at them.

The other site has a good blow up of the system, like something out of an old J. C. Whitney catalog.

You might also contact the Classic Center. They would know where to get these parts if anyone would.