Hey, Steve! Nice find!
To address your inquiry, it's called a "multi-pin connector." (It appears to be way too big to be a DIN connector, which is a kind of multi-pin connector, an example of which is the connecting cable on the Chrysler cassette player/recorder, circa '71, as was in your hemicuda convertible.)
As far as sources are concerned, perhaps try contacting Parts Express, as they may be a source for what you need, or, if not, be able to provide a helpful suggestion.
https://www.parts-express.com
My only other thought, if the above is not viable, is to search for a complete non-working unit which you may be able to acquire on-the-cheap, simply for it's parts. (I hope that this helps.)