dont know if this helps or not but could u call it a different name? apparently when i was little i wouldnt drink water but..... i would drink tapolena (aka - water from tap)
maybe worth a shot?
My 28 month old son wouldn't drink it either. It is very important not only for calcium, but for the vitamin D. I got my son to drink it by adding Nestle's strawberry Quik to it. He wasn't a fan of chocolate milk...imagine that. He loves the strawberry. I just squirt a little in and he drinks it like crazy. In fact, he would rather have that than juice. Buy the liquid type that you squeeze. The powder is clumpy. Also, it is fortified with calcium and has less sugar than a lot of the juices on the market today. Good luck!
There is lactose milk and calcium supplements. I've been lactose since I was little and my mom used to just give me the supplements.
Keep giving the chocolate milk if he will drink it, and increase his dairy in other areas!! Yogurt, cheese, cottage chesse, ice cream. Maybe have him take a mulit vitamin so just in case he is lacking anywhere!!