KLH model 9 electrostatic Speakers

By the way the speakers are using two prong only...

Many manufacturers makes C7 power cords. Wireworld, Cullen, Pangea to name a few. I would check those out and see if you find anything you like. 
Additionally some cable manufacturers like Triode Wire Labs will make custom power cables for you. 

Kingdeezie thanks , I will appreciate your search and recommendations..

David JansZen rebuilds and sells them in Columbus, OH. They were designed by his father. He can answer any question.
https://janszenaudio.com/pages/klh-nine

If you just need a C7 I have and like a WireWorld.

Thanks Fuzztone