The place is called speedway motors.
They also sell stainless ones and also polished stainless.
These cast iron units are $299. The stainless are $399 and the polished stainless are $499.
Here's a link. If it doesnt' go directly to the 2nd page of their "headers and exhaust section" you can navigate around pretty easily and find them.
http://www.speedwaymotors.com/Classi...irst_answer=17
I noticed they also sell a chrome louvered exhaust cover for the ram horns. Not sure why you'd buy the ram horns and then cover them up, but they do look pretty cool to me.