The Akrapovič website has them listed as archived which means they are no longer produced. Your best bet is to contact your local Akrapovič distributor and see if they have any old stock left. The other option is to try and find a used one on eBay or in the parts section on here.
You know, I wanted the hex shape can for my own bike, but I found a smoking deal on the Oval version. It's grown on me to the point where I prefer the Oval can for the older generation (03-06) cbr. I prefer my akrapovic over any other brand, but if I were in the market for a full system right now I wouldn't pass up an arata, arrow, sato or Leo vince.