The main question is (and I am not familiar with your model tractor) whether there is some kind of interaction with DEF or antipollution device or sensing involved with that muffler. Unless there is some complexity of that nature the second question is "How much do you care what it looks like?" So long as it is simply exhaust gas in and exhaust gas out you can go find any muffler that fits (or almost fits) and adapt it to the tractor. If it is purely a muffler only a blithering idiot, a wealthy one, would pay $700 for a muffler.
Update: I see a photo I took of an M8560 several years ago. It looks like a simple vertically mounted, out in the open muffler. About as simple as they get & very accessible. I'd whack it off and put on a new one in a sensible price range. Being out in the open and exposed as it is it may be worth looking around for something made of heavier/thicker metal.
