I haven't found one yet, altho admit to not looking overly hard as I not a huge fan of hot chocolate.
but
when I am in need, I have melted some of the chocolate I can have (ie, green and blacks 70%), added hot milk, then topped up with some hot water adding sugar to taste.
tis rather nice
(BTW, thortons do a tub of chocolate flakes that you can sprinkle on top of creamy hot choc, and the ingredients say no milk etc......they can also be made up as above into a chocolate drink)