The G25087-001 cable comes with our Intel® Server System P4304CR2 or in our P4000L chassis. This cable is part of the power distribution board and it is not offered as a separate item.
For 6+8 pin you can use:
(comes wit 4 x cables)
But Intel does not provide any 2x8pin solution (=300W) as the limit is around 225W per cable.