Are we talking about the cat converter to y pipe gasket in the exhaust system, only a ferw vendors here will have it, not a parts store item to my knowledge.
If you can't find the gasket try some of the high temp rtv(silicone)
I used it on mine 2 years ago no leaks yet. I did make sure both flanges
Were nice and clean and they were real flat no gaps around the
Edges