I have compiled a list of sources for the elements that are available to the amateur chemist. Calcium will be discussed here.
Calcium is a somewhat soft, silvery-gray metal. It reacts with water to produce white calcium hydroxide and hydrogen gas. Calcium compounds are very common in the earth. Calcium carbonate is found in calcite and mollusk shells. Calcium phosphate is found in bones. Calcium as a metal has fewer uses.
In element form: Some lead acid batteries use a 0.1% calcium alloy.
In compound form: Calcite, aragonate, and mollusk shells contain calcium carbonate. Bones are made of calcium phosphate.
Here is my sample of calcium metal. It was purchased for $13.00 from GalliumSource.