There are aftermarket stainless steel header pipes and I think some that are double-walled, like Monte said. I lot (most) of your jap bikes use (or used to use) double walled pipe. Until the later part of the 20th century BMW engineers seemed obsessed with weight and it seemed every year the bikes would shed a few pounds. It seems this thinking went out the window once the Ks and Oilheads took over...