You can get them from British Customs.
http://www.british-customs.com/triumph-america-speedmaster-efi-bomber-exhaust.html
They do sound good. They are also a bit pricey. Can't use them if you have a center stand as the "hidden" mount uses those mounting holes.
Stainless Ride also has a good sounding exhaust.
http://www.stainlessride.com/mufflers/triumph/america/2008-2012-efi.html/

09 America, some modifications