Here’s a snippet from Harvard Health:

The body gets the calcium it needs in two ways. One is by eating foods or supplements that contain calcium. Good sources include dairy products, which have the highest concentration per serving of highly absorbable calcium, and dark leafy greens or dried beans, which have varying amounts of absorbable calcium. Calcium supplements often contain vitamin D; taking calcium paired with vitamin D seems to be more beneficial for bone health than taking calcium alone.

http://www.hsph.harvard.edu/nutritionsource/calcium-full-story/

Yes, they too indicate that humans can get their calcium from the cow (via dairy products) but they also suggest dark leafy greens, although they do indicate that dark leafy greens and dried beans are potentially good sources as well. Although they did mention that you would need to eat the “right” beans and greens as they specifically stated that only those beans and greens that offer highly absorbable calcium would suffice.

Short of that, they suggest supplements. So if you aren’t willing to eat the proper beans and greens,
you could take calcium supplements; directly or via the cow. ;-)

Me, I have my dark leafy greens in my daily morning shake, with almond milk.
http://veganbits.com/kale-smoothie-issues/#.U48Yu7VOXL8