Mother's Milk is one of my favorite commercial brews. I was looking for something similar and couldn't find a clone of it. Settled on a cream stout kit. Would love to hear how it turns out if you do find one.
Just finished drinking a keg of chocolate milk stout that came out close to Mother's Milk. It was a kit from Northern Brewer. To get it closer, I would leave out cocoa nibs and use another 1/2 pound of dark steeping grains.