Calcium can be obtained from a variety of plant-based sources such as green leafy vegetables and legumes. Beans, broccoli, Brussels sprouts, collards, kale and mustard greens are excellent sources, as are calcium-fortified plant milks.
Dairy industry advertisements suggest that drinking milk results in stronger bone density. However, a study at Harvard University found little evidence of the supposed health benefits of dairy, and questioned the methodology by which U.S. dairy guidelines were determined.
There are also a number of health concerns about dairy, which you can read about here on the Physicians Committee for Responsible Medicine website.