Calcium is a mineral, and vegans get their calcium from plant sources (just like the cows do). Some of the richest sources of calcium are leafy green vegetables such as silverbeet, spinach, watercress, dark green lettuces, kale and broccoli; almonds and other nuts; sesame and other seeds; and beans.
Listen to this very informative podcast episode by Colleen Patrick Goudreau about Calcium: Where do I get my calcium if I don’t drink cow’s milk?
There are foods that are fortified with calcium such as some tofu or soy milks, but they are not mandatory if one is consuming enough of a variety of the whole plant food sources mentioned above. General guidelines indicate we need about 1000mgs a day of calcium, which can easily be met with a balanced vegan diet.