ANSA makes the final muffler, which I guess is really the resonater. It is part number ME 0897.

I know the front down pipes are NLA, but I think the rest of the system is still available if you look hard enough.

A good muffler shop can make the pipes you need. Just finding the center muffler and the resonater will be the tough part.

ANSA might also still make the muffler. BOSAL would be a good place to look but I doubt they would carry a stock muffler as they tend to be more of the stainless performance type of thing.