I have compiled a list of sources for the elements that are available to the amateur chemist. Niobium will be discussed here.
Niobium is a silvery gray, high melting metal from Group 5. It is quite reactive but is protected by a layer of niobium pentoxide. Because of this, niobium is extremely corrosion resistant. Niobium ores are commonly found along with tantalum ores, and the two elements were repeatedly confused in their early days. Niobium forms pentavalent compounds that exist in non-aqeous solution, including the yellow and low-melting pentachloride. Niobium has a relatively low density for a refractory metal.
In element form: Niobium jewelry, because it is hypoallergenic, is quite popular. The wires leading into the arc tube for high pressure sodium lamps are made of niobium metal or 99% niobium alloy. Some steels have small amounts (0.1%) of niobium in them. Niobium capacitors, while rare, replace tantalum capacitors in some applications.
In compound form: Lithium niobate is used in some piezocrystals. Niobium pentoxide is used in some ceramic capacitors.
Here is my sample of niobium metal. It is a mispunched niobium disk sent gratis from Reactive Metals Studio upon request.