How to quiet down a lgt25k54 Usqvarna Tractor....?

Looking for ways to quiet down a lgt25k54 with a 25hp Courage twin motor. An aftermarket muffler doesn't seem to be an option but if someone could point me in the right direction that'd be great. Looking for ideas and or solutions.
Thanks

http://www.kohlerengines.com/onlinecatalog/pdf/32_690_01_EN.pdf

http://kohlerengines.dirxion.com/app.php?RelId=6.4.7.1&bookcode=kea14flx see page 36, your engine model is sv730.

https://www.google.com/webhp?sourceid=chrome-instant&ion=1&espv=2&ie=UTF-8#q=kohler muffler 3206801s shop for best price.

https://www.google.com/webhp?source...espv=2&ie=UTF-8#q=kohler muffler kit 3278601s again, shop for best price.