How low in fat?
most of your standard milk chocolate is going to have about 12% liquor by default. you want a milk chocolate that has 1/2 the fat of standard milk chocolate? if so, while it's technically feasible, you're simply not going to find any supplier who has the knowledge or desire to do such a thing i'm afraid. about the lowest commercially available milk chocolate - finished fat level - that your'e going to find (assuming you want to enrobe or mold with it) will be about 28% ish.
Do you know which chocolate would be in that range?
Call the fine folks at Cargill or Blommer and they can walk you through what their current offerings are..