And your chances of finding a good one are not much better than winning the lottery twice, without a ticket.
The first bit that falls apart is usually the muffler.
Mower engines are not tuned so the muffler is not particulartly important for any reason other than preventing fresh ait contacting the exhaust valve and burning it
I am jet to find a twin cylinder one where the exhaust pipes are actually fixed into the muffler.
So any mower muffler that is the right dimensions can be made to fit but it can be a big job to do it .
Mufflers ar part of the mower in most cases so are quite expensive because of low volume production