I have compiled a list of sources for the elements that are available to the amateur chemist. Cadmium will be discussed here.
Cadmium is a soft, blue-gray metal that is considered borderline between the transition metals and the post-transition metals. Like the post-transition metals, it forms primarily one oxidation state, its compounds are generally (although not completely) colorless, and it is soft and low-melting. However, it is in the d-block, so it is technically a transition metal. Cadmium is toxic and replaces zinc as a heavy metal poison. Cadmium is moderately reactive (more so than mercury but less so than zinc), so it dissolves easily in hydrochloric acid, forming hydrogen and a colorless solution. Cadmium sulfide, however, is bright yellow. The oxide can be brown (the other form is white), and the selenide is red. There are few other colored cadmium compounds.
In element form: Nickel-cadmium batteries supposedly contain cadmium metal at the anode, but I have never been successful in extracting any cadmium from a "sub-C" cell battery. Little rechargeable button cells (LR1130) contain a gray paste at the anode that is probably cadmium metal mixed with a binder. Cadmium plated bolts and screws used to be relatively common, and can be distinguished from zinc by the increased softness of the coating.
In compound form: Cadmium sulfide was used in cadmium yellow pigment, but has been almost completely discontinued due to toxicity. Cadmium sulfide is still used in photodetectors as the orange line separating the two electrodes because of its change in conductivity due to light.
Here is my sample of cadmium. It is a cadmium plated screw, found amongst hundreds of other screws by scratching the coating with magnesium metal. Cadmium plating typically has the dull bluish-gray appearance, somewhat like hot-dipped galvanized zinc. This is probably due to aerial oxidation.