For resources and help with that you should best contact their minority organizations in Serbia. Information on such organizations you will most accurately obtain through Russian embassy.http://www.ambasadarusije.rs/ru/soot.php
For these migrants, many documents and materials are available in historical archives in Serbia.
You should also try to contact through Russian Orthodox Church their temple of the Holy Trinity in Belgrade that was built in 1924. by the refugees from Russia and still serves this community.http://www.mospat.ru/ru/
According to the current priest who is himself from one such family, they have kept records of the congregation.http://www.politika.rs/rubrike/Drustvo/Na-komadu-ruske-zemlj
EDIT: A book in Serbian you should look for:
"Russian Refugees in Pančevo 1919-1941".
The author has extensively studied the records of the Russian Orthodox church in Belgrade and the community.http://www.srpskadijaspora.info/vest.asp?id=6879
"Rodoslovlje" Serbian Genealogy Societywww.rodoslovlje.com