Good question that only HK can answer I'm afraid. It took me over a year to get one for my P2K .40 in .357 SIG and I too have been looking for one for my SK .40. I have no idea why they are not getting extras in but I imagine it has something to do with HK Germany not releasing them. HK-USA is pretty much as the mercy of HK-Germany. They do what they want and no matter how much HK-USA orders something, if HK-Germany does not want to ship it they won't. How CDNN got them, Lord only knows. I would be interested in knowing if the extra barrels were without serial numbers indicating they were "parts" barrels, if they had serial numbers not matched to the pistol which would indicate they were taken from parts guns, or if they were actually serial numbered to the pistol by HK, which I have not heard anyone claim that they were.