Once I have discovered how to make something myself, I typically stick to doing it that way from then on. Hot chocolate mix is no different. Have you ever looked at what is in commercial mix? Bleck, and I can't even pronounce all of the names on the list.
Here is the recipe that I use, there are quite a few out there floating around all very similar. I really like how it isn't sickly sweet. The first time my kids did comment on how it was not as sweet as they were accustomed to, but after that I haven't heard a peep. It is obviously what you are used to.
10 cups dry milk powder
4 ¾ cups sifted powder sugar
1 ¾ cups unsweetened cocoa powder
1 ¾ cups powdered non-dairy creamer
Combine together and store in an airtight container. This makes about 15 cups of mix which is roughly 45 servings.