First, I would say that there is no need to be excessively concerned about calcium. Hunter-gatherers and animals don't need to drink the milk from another species to build strong bones, and many cultures don't use dairy, without having a high incidence of bone fractures or osteoporosis. The RDA for calcium seems high, but it has been calculated considering that most of the calcium is from dairy (and only 30% of dairy calcium is absorbed). Moreover, the average american ingests some phytates, salt, perhaps has an inadequate intake of vitamin D and of magnesium, etc. On the other hand, it may well be possible that wild plants are more nutrient-dense than cultivated ones; that paleo humans got more sunshine (hence more vitamin D), more exercise, etc. I don't know. Probably calcium supplements are not necessary, but if you do choose to take some, then it's necessary to balance with other minerals (like magnesium). Now, what green veggies to eat? My philosophy is: eat whatever you like; besides calcium, they contain many more nutrients. But to have an idea, here is the amount of calcium (in milligrams per 100 grams) for a few foods. I didn't include spinach (which contains a lot of oxalates). Nuts and dark green vegetables are the richest in calcium; meats and fruits contain little calcium. almonds 266 turnip greens 190 kelp 168 collards 145 parsley 138 kale 135 broccoli 48 lettuce (romaine) 36 Note 1: 100 g of "kelp" includes about 80 grams water. Note 2: I forgot which foods contain oxalates (the two main ones are spinach and rhubarb). JL