That looks like the one I pulled off my first 70 Challenger that I bought off the original owner in 1978. It may have been available at Chrysler dealers.
Here is one of the pictures of the car when it was new pulling a trailer. It is kind of a different car in that it was bought b y a military member as an international export car and he brought it back with him. I still have the original title from Morracco.
I had the same hitch on my 71 Challenger. I am the second owner of the car. The original owner said the hitch came with the car. Unfortunately, I no longer have the hitch. Now that we know how to read buildsheets, I see my car came with a towing package. Your hitch might be one of the hitches Chrysler sold out of its accessories catalogue for the towing package.