Furthermore, they are almost always found as mixtures, usually including other metals, particularly thorium (radioactive). There's not that many places where the concentration of the metal in the ore is worth the cost of the extensive recovery process. Recently, old tailings from iron and titanium mines have been processed by acid leaching to recover some REEs. Thorium tailings should be an even better source, but they aren't all that common either.
ALL of the REEs are more common than any of the platinum group metals, silver, gold, cadmium (used to plate tools), indium (used in touchscreens), mercury, or bismuth. But almost all those elements are found in concentrated ore deposits, or can be recovered as a byproduct of processing other metals on a large scale, such as zinc and copper, where the flue dust, electrorefining sludge, etc. are effectively "ores" of elements not found in rich deposits, such as germanium, gallium, indium, selenium and tellurium (almost as rare as gold or platinum) -- as well as gold, silver, and platinum group elements.
Unfortunately, mines have often gone after only one or two metals and discarded everything else. Now investigators are going back through their old dumps to see which ones contain other valuable metals. There are tons of coal ash available as well, but I suspect it's [link:file:///Users/SHN/Desktop/fs2015-3037.pdf|so full of silica, alumina, and lime] it's not worth the effort.
https://en.wikipedia.org/wiki/Neodymium#/media/File:Elemental_abundances.svg
(Just to let folks know that all the "easy" solutions have already been considered. 
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