Check Ebay and Craigslist.
You can also do a check at Bike Bandit. They have an OEM section where you can look up bike parts. Check several years before and after your year. If the part numbers are the same, then you will be able to use an exhaust pipe and muffler from a different year.
You may be able to modify an RM pipe and muffler to fit, but you would have to know someone with some welding skills that could modify the mounting brackets.