you won't find an exact replica of the 550F muffler. also a stock used one is very hard to find, it will be a long search. if you really want a stocker, probably the best thing is to get a temporary replacement and then keep looking for one.
if you are willing to replace the whole system then delkevic makes an alternative at a very fair price.
but you probably want to keep the original header which is a very characteristic design, right?