Other Users in the past have also mentioned trying to getting replacement cables for the Wraith CPU Coolers. But it seems like it isn't sold separately.
You can either purchase a used Wraith Max in Ebay or see if someone in Ebay will sell you the cable separately.
If the Wraith was under Warranty maybe you can ask to see if AMD will send you a spare RGB cable. If not you are out of luck since the AMD CPU Cooler cables aren't sold separately.
