Most living beings contain calcium, including all plants, but in quantities that are too small for the needs of anyone who has a calcium-based skeleton, unless you eat daily larger quantities of plants than are practical for most humans (e.g. eating between 1 kg and 2 kg of nuts each day, depending on what kind of nuts they are).

Dark leafy greens are not "quality sources of calcium". One would need to eat several kilograms per day. No human does that. The quantity that needs to be eaten is greater than it could seem from the elemental analysis, because a part of the calcium will be lost during cooking and another part will remain bound in insoluble compounds that will not be absorbed in the intestine. Moreover, eating many kilograms per day of dark leafy greens is guaranteed to cause health problems due to oxalic acid and other substances that are present in excess.

All the studies that I have seen have shown that the vegans who do not take calcium supplements have significantly less amounts of calcium in the body than non-vegans and are more prone to osteoporosis.

This kind of false information about plants that are "quality sources" of substances that are really deficient in all plants is very dangerous for vegans. Any vegan must take up to a dozen supplements to maintain optimal health and those who are not aware of this develop sooner or later various health problems and many go back to a traditional diet, without understanding what they did wrong.

You would have to eat like 5 cups of legumes every day to get enough iron that way if you're a woman. That's almost two pounds. Nuts or greens would be an even higher amount.

In New Zealand where cows are all grass fed, they eat 50 kg of grass each day. Milk is concentrated nutrients.

Having much calcium among vegetables does not mean having enough calcium as a human food.

Your link uses the silly "cup" unit of measure from which it is hard to assess which is the real calcium content.

The right way to show the content of a nutrient in some food is to show how many kilograms or pounds you must eat daily to provide enough of that nutrient.

In the case of calcium the best case that I have seen for various vegetables is that you would need to eat at least 1 kilogram per day, based on the elemental analysis.

However this is far too optimistic, because when cooking the vegetables a part of the calcium may be lost and another part will be bound in insoluble compounds and it will not be absorbed in the intestine after eating.

So a more realistic estimation is that even for the vegetables with the highest content of calcium you might need to eat at least 2 or 3 kg per day.

For nuts and legumes it is impossible to approach even 1 kg of daily intake, as that would include too much energy in starch or fat.

So only leafy vegetables would avoid gaining weight, but eating kilograms per day would be not only unpleasant, but also harmful.

I happen to be a vegan, so I have studied carefully my alternatives and the best for me is to add some calcium phosphate powder to my food, together with the table salt. I use phosphate and not another calcium salt, because even if all seeds and nuts, including all legumes, have large amounts of phosphorus, most of it is contained in phytic acid, which is harmful, so I use preparation methods that remove much of the phytic acid, but they also remove most of the phosphorus, so I compensate that by adding the calcium as calcium phosphate.