Perhaps Serbs too may be among the Indo-Europeans coming out from Gangatic plains during ancient times, albeit a lot of water has flown since then:
http://voi.org/books/rig/ch7.htmQUOTE>> 2. ANUS: Iranian, Thraco-Phrygian, Hellenic.
a. Iranian: In the Avesta, in Fargard 19 of the VendidAd, it is an Angra {ANgiras} and a Druj {Druhyu} who try to tempt Zarathushtra away from the path of Ahura Mazda.
The priests of the Iranians were the Athravans {AtharvaNas = BhRgus}, and the words Angra and Druj occur throughout the Avesta as epithets for the demon enemies of Ahura Mazda and Zarathushtra.
b. Thraco-Phrygian: While the Armenians, the only surviving members of this branch, have not retained any tradition about any of these priestly classes, it is significant that one of the most prominent groups, belonging to this branch, were known as the Phryge {BhRgu}.
c. Hellenic: The fire-.priests of the Greeks were known as the Phleguai {BhRgu}.
What is more, Greek mythology retains memories of both the other priestly classes, though not in a hostile sense, as the names of mythical beings: Angelos {ANgiras} or divine messengers, and Dryad {Druhyu} or tree-nymphs.
3. DRUHYUS: Baltic and Slavonic, Italic and Celtic, Germanic.
a. Baltic and Slavonic: The word Druhyu occurs in the languages of these two branches in exactly the opposite sense of the Vedic Druh/Drugh/Drogha and the Iranian Druj. In Baltic {eg. Lithuanan Draugas} and Slavonic {eg. Russian Drug} the word means “friend”.
b. Italic and Celtic: While the Italic people did not retain the name of the priestly class {and called their priests flAmen = BrAhmaNa}, the Celtic priests, as we have seen, were called the Drui {genitive Druad, hence Druid}.
A significant factor, showing that the Celtic priests must have separated from the other priestly classes before the priestly hostilities became intense, is that the BhRgus appear to be indirectly remembered in Celtic mythology in a friendly sense. <<UNQUOTE
So DRUHYUS are most likely candidates.