Lots of dark greens.

Or fortified sources like calcium infused orange juices or nut milks, or taking a plant based calcium supplement.

If the green aren't doing enough (or you can't consume that much greens a day like me), you have alternate choices too.

You can purchase calcium supplements if it is a concern to you. I personally take multi-vitamins that supplement my diet and take the occasional Emergen-C packet for calcium and vitamin D (http://www.vitacost.com/alacer-emergen-c-vitamin-d-and-calcium-fizzy-drink-mix). One packet provides 50mg calcium (50% daily value).

I found that without supplementation, my typical daily diet only provided 20-30mg of calcium without consciously trying to reach optimum calcium intake. You can use MFP to track your diet over the course of a week and find out how much you'd like to supplement each day and figure out a plan of action from there.

I was doing well with calcium until I gave up the soy/nut milks. Now I have a vegan calcium supplement that takes care of 50% of my daily value, & I can get the rest with dark leafy greens & fortified orange juice in a smoothie each day, along with my other whole foods. I definitely had to have the supplement though to take care of that first 50%.