Hiya. Delkevic's one of the more popular ones for this bike, readily available on eBay or through the Delkevic website. I'm pretty sure there's a Vance & Hines that will work as well, plus with some fabrication work I'm sure there's more options. But those are what I know of, for slip-ons.
There's a lot of info here in the forums, check out that Search feature and see.