Bill,
I think you mean a "Bisson" muffler. Here's one solution. If you can provide the bortherhood with the dimensions, Bission will make almost anything you want to your specification. They charge very little extra for custom work. Also, almost all of the standard mufflers on their website come with a set of dimensions. I would look for something close to yours to get some idea of price.
I have has serveal custom mufflers made over the years and they do a great job. The easiest way is to make a drawing of exactly what you want and e-mail it to Janet.
http://www.bissonmufflers.com/en/index.html