I have compiled a list of sources for the elements that are available to the amateur chemist. Gadolinium will be discussed here.
Gadolinium is one of the more corrosion-resistant rare earth metals. In other words, it does not need to be kept in an ampoule or under oil to prevent rapid corrosion. Its trivalent compounds fluoresce green. Gadolinium compounds themselves, however, are white and boring.
In element form: No sources found.
In compound form: Some green phosphors contain gadolinium doped compounds.
I do not have any gadolinium samples at the time of this writing.