Yamaha are in exactly the same position you are... This is a CUSTOM cable. They can no more buy it cheap at an 'off the shelf' cable manufacturer and gouge you than you can find it yourself...

You might want to consider that most DIN cables are designed for signal levels, and not for speaker level. They may be using higher gauge strands that your average DIN cable. Personally, I'd simply buy TWO of these Yamaha cables and rest happy knowing you have a backup if the same thing happens again...