Ok, not a REAL chocolate wine but I thought I would share the following:
I got some "Stevia" from the health food store. Stevia now also comes in chocolate flavor.
Soooo, I thought, why not add some to a glass of some of my not so great wine. To my surprise it was quite good. You could definitely taste the the "chocolate" flavor. I used two drops but I think you could use only one and tell a big difference. If you have some wine to experiment with - or if you just like chocolate, you might give it a try. It is probably definitely easier than trying to make a chocolate wine from scratch.