I just got a new to me 81 KZ1300.
The exhaust is just about rotted off at the collector so I went searching for a 6-1 header. I had one on my 79 which I stupidly sold in 2001. After casting about on the net it seemed they were no longer made and very hard to find.
I was able to find the company that originally made mine... DG Performance.
Called them up today and spoke to a very nice fellow named Mike. It turns out they had none in stock but they will be making me one and it should be ready in the next few weeks. I was thrilled! I remember how good mine used to sound with it on.
So, it turns out they are still making them and they are very reasonable at $700 US.
dgperformance.com/