Not sure what you need. This is for your 67, right? I thought there was a handle on the vent that you turned 1/4 turn to unlatch the door. Where is this cable you're talking about?
He's talking about the vent under the dash on the driver's side (footvent). I dont know where to find one either, mine was missing when I bought the car, so I'd be interested if anyone knows where to get one also.