[The Might]

Now, it is possible that others remained in Valinor, but reading through Sharkû's essay linked above I rather tend to believe that the Heren Istarion was, as Sharkû very nicely shows, only an ad hoc organization formed only to help the free people of M-e get rid of Sauron, and that the order mentioned in the quote from the UT actually is that of the Ainur.

Again, I highly recommend reading the essay. The idea that other groups of Ainur under the leadership of others then Curunir made their way to other regions, for example the south of M-e is unlikely as showed in the essay. Again unlikely, but not impossible.
Still, I don't see why we should think there were any others as long as others were never mentioned.