Hate to say this, but if your muffler need replacing then there is a very good chance that the rest of your exaust piping is going as well. At least that has been my experience. Almost any independant shop that specialises in imports should be able to get you an OE equivalent for about half the OE price based on my experience in my area (NW Ohio). Your mileage may vary, of course.
Zenmervolt
EDIT: Grammar, coffee's losing its effectiveness.