If a space station were to be built in the outer solar system, is there an asteroid beyond Jupiter with a ratio of rare earth elements high enough to make it worthwhile to mine for the rare earth elements, to supply this space station with those materials it needed?
We don't know if there is such an asteroid made of decently concentrated rare earths, for the simple reason we are not able to survey all the asteroids for this.
Of course you can postulate the existence of such a body, which can be found and used by the crew. Just make sure that the abundances make sense, in other words 500 tons of pure Gadolinium are less credible than 500 tons of other metals with a few percent of Gadolinium in it.
Research on Ceres indicates that cryovolcanism causes water ice to seep to the surface, where it sublimes and leaves salt deposits. We have not analyzed these deposits yet, but they are practically guaranteed to contain concentrated useful elements. This is similar to Earth where salt flats are important mining resource.
Farther there it is too cold and water ice is too hard, but there too are geological processes with nitrogen ice. If you remember the first photos of Pluto by New Horizons, the surface shaped by active geology was a great surprise. And active geological processes means that rare elements get dredged up and eventually concentrated in veins/deposits like they do on Earth.
I believe we can safely say that all dwarf planets have active geology in some form and thus interesting deposits. Many moons too, even if they are smaller they can still can have geology powered by tidal heating.
Rare Earth elements aren’t rare, however separating them is difficult. On Earth, most ferro-phylic element were drawn into the Earth’s liquid Iron core. The Gold and other heavier elements (like rare earths) in the Earth’s crust came from ‘late great meteor bombardment’ after the Earth solidified. Otherwise the solar system abundance of elements depends on 1.) nuclear stability and presence in solar fusion reactions and 2.) the peak nuclear stability of Iron/Nickel (higher elements not created by solar fusion, only in supernova). Carbon and Oxygen are common because they are part of the CNO fusion reaction. Lithium (Deuterium, Beryllium, etc) is not common because it decomposes at solar fusion energies. Answer: The Earth was lucky to have Rare Earths, unlikely in the outer solar system.