First I don't know where to get a new black connector.
I DO recall seeing a 75 Roadrunner 318 (that's the one that looks like a Cordolba) with the black connectors, which I noticed because my 73 Challenger had white. I had always thought the black connectors were a mid 70s thing and the white was the the original look for an ebody. But that is just what I thought. If you want the black, maybe look for a junk 75 Cordolba or Roadrunner because that's what I saw the black connector on. At least one of them had it anyway.