I have compiled a list of sources for the elements that are available to the amateur chemist. Barium will be discussed here.
Barium is a soft, silvery gray metal of the alkaline earth metals. It is the heaviest member of the group that is not radioactive, and also the most reactive. Barium metal reacts vigorously with water, producing soluble barium hydroxide. Barium easily absorbs oxygen and nitrogen from the air when heated. Barium is quite toxic in its ionic form, making it useful as a rat poison.
In element form: Barium metal is used in vacuum tubes and CRTs to absorb any leaking gases. It is visible as a reflective crown on the inside of a tube, but probably not visible in a CRT.
In compound form: Barium sulfate is used to map the digestive tract because it is opaque to X-rays. Barium ferrites are used in credit card magnetic strips. Electrodes in fluorescent lamps are coated with barium oxide to increase the emission of electrons. The screen of a CRT has barium oxide in it to help absorb the radiation.
Here is my sample of barium. It is a vacuum tube obtained from a friend who has a stock of them. The barium is visible on the right side.