Hi, J.,
Find other foods with calcium and vitamin D. There are a lot of calcium-fortified juices out there. I'd suggest kale, too, but not too many kids like that stuff. If your son will eat foods that have milk in them (cereal, mac & cheese, cheese sticks, yoghurt, milk-based soups), stick with those, and make drinking milk an available option, but not a chore.
If your son will not eat or drink anything that has milk in it, you might want to get him checked for a food sensitivity or allergy. I was allergic to milk as a child, and I didn't like to drink it or eat cheese because it gave me horrible sinus headaches and sore throats. My doctor put me on calcium supplements until I outgrew the worst allergy symptoms around age 11.
I'm still not a milk drinker, though. My son enjoys Horizon Organic Vanilla Creme flavored milk as a treat, and he was able to transition from that to regular milk at kindergarten, even though he hadn't been exposed to the idea of drinking milk with a meal.
Good luck!