I have compiled a list of sources for the elements that are available to the amateur chemist. Terbium will be discussed here.
Terbium is one of the less reactive rare earth metals. It forms trivalent compounds, white and boring. Terbium also forms some divalent and tetravalent compounds, such as terbium (III,IV) oxide, which is black. Terbium compounds fluoresce green brightly. Higher valent terbium compounds are strong oxidizing agents.
In element form: Terfenol-D, an alloy used in Soundbug(r) speakers, contains terbium, dysprosium, and iron.
In compound form: CFL bulbs and CRT tubes contain green phosphors, most commonly made using terbium doped yttrium oxide or some other terbium doped compound.
Here is my sample of terbium. It is a CFL bulb.