Green leafy vegetables, soy, sardines, soups cooked with bones in them, seaweeds, and acidified calcium supplements such as calcium malate or citrate. Avoid supplements with calcium oxide/hydroxide and calcium carbonate (oyster shell, coral, dolomite).

Kefir is not necessarily a good calcium source, but the intestinal bacteria do aid in the absorption of calcium due to the acids they form, which make minerals more absorbable.

Dairy is also a bad source for calcium as the calcium absorption is blocked by the protein in the milk.

Also keep in mind that silica is MUCH MORE important than calcium for bone strength. And it aids in calcium absorption as well as is responsible for putting calcium in the bones.