I have never seen the wire set sold separately, but maybe you will get lucky and find one. Since the 25A all the way to the 60A use the same setup maybe you can find someone with a burned up ESC that will be willing to sell you the wire set. If not, it should not be difficult to wire in your own switch and receiver harness.
Looking at the ESC with the battery positive on the left and the batt. negative on the right, the order goes as follows from left to right:
Switch neg(black), sw. pos.(red), receiver signal(white), rec. pos.(red), rec. neg.(black)