I have compiled a list of sources for the elements that are available to the amateur chemist. Rhodium will be discussed here.
Rhodium is commonly regarded as the most expensive non-radioactive element in the world. (Some radioactive elements require millions of dollars to create one or two atoms, so they cannot be accurately compared to the stable elements.) Rhodium is a hard white shiny metal that forms an excellent plating on materials. This plating is ironically used in cheap jewelry because the amount of rhodium used is extremely small. Rhodium forms a wide range of aqueous oxidation states and complexes, like many other precious metals.
In element form: Much jewelry is rhodium plated and it is often advertised as such because it makes it sound valuable. Catalytic converters contain rhodium mixed with platinum which is what makes them so expensive.
In compound form: No sources found.
Here is my sample of rhodium. It is a reed switch advertised as having rhodium-plated contacts.