psu power cables

I have just received my new GPU that requires two 8 pin power cables I have the Corsair HX750 Platinum PSU Unfortunately due to breaking up with the ex and moving out of the house I have lost my spare cables. My mate has a spare 8 pin power cable from his Inwin PSU Can I use this in conjunction...

I recently bought a new GPU for my rig. Its an RTX 580. It has 1 (6+2)PCi e slot. My power supply has 2 (6+2) slots. And it is impossible to find the correct (6+2) male to (6+2) male power cable. Please help me!