What engine do you have?

Just about any standard muffler for a full size V8 will give you the quiet you desire.  A Walker Dynomax #17749 would certainly do the trick, but that has 2 1/2 inch inlet and outlet pipes, with a six you could get away 2 inches or even 1 3/4.  Check out the Walker website.  The main thing is length, the longer, the quieter.  The 17749 is 20 inches long.

Thanks for the help, and I did post a pic but I can't seem to find it???!!!