This is probably not what you want, but you could make some with fair trade chocolate bars or chips: https://bakingmischief.com/easy-chocolate-sauce/
That recipe is basically a ganache, which you can make thicker or thinner (with less or more cream) or add sugar if you want it sweeter. You can tweak it to your liking and make a batch that would last you a week or so and store it in the fridge.
There are also recipes for chocolate sauce that use cocoa powder, but I don’t know how hard it is to find fair trade cocoa powder.
Mix some powdered baking chocolate with powdered milk and maybe sugar if you want and store it in a mason jar. Add it to your coffee when you want. You can always dissolve it in some water to ensure any lumps are removed beforehand.
I know Hershey’s has a simply 5 that is HFCS free or Santa Cruz brand… I’m not sure (I know Hersheys isn’t) but if the Santa cruz is fair trade.
I feel like your best bet may be to make your own? It’s fairly easy and lasts awhile in the fridge - that way you have control over the ingredients.