Seeing recently the introduction of Diet Chocolate Cherry Dr. Pepper I was curious if they made a non-diet version.
No deal.
That reminded me of one of the only other chocolate sodas I have ever seen.
Canfield’s Diet Chocolate Fudge. Also not available in non-diet form.
So why are there no regular chocolate sodas marketed?
Aw, man. Mention of Canfield’s Diet Cherry Chocolate Fudge soda brings back memories of growing up with my best friend Steve, who was diabetic. This was in the days before Aspartame, so his house was always full of sodas that tasted like ass (e.g. Canfield’s) and candy that gave you the shits (hard candy with sugar alcohols). Good old Steve. 
ETA: sorry for the unproductive tangent
Oh, man, I forgot how good Canfield’s was until I saw this thread. Haven’t seen the stuff in years.
Other than that, I’m useless to answer your actual question.
There was definitely a chocolate soda I drank at the pizza store when I was a kid, in the late 80’s/early 90’s. I can’t remember the name - Best Health? Health Best? Something like that. It couldn’t have been diet, because I wasn’t supposed to drink diet soda as a kid, and have never liked it.
ETA that it may have been a regional thing; this was in New Jersey.
'Cause people who aren’t on diets have better ways of getting chocolate?