As Dakeyras said, there's no official, concise, complete Eastern European setting for D&D.
However, with a little effort , you can create your own, based on fragmented D&D resources and material for other rpgs, both of which will require conversion... but as a GM/DM that shouldn't be too much of a challenge.
I'd suggest taking a thorough look at the rather cool GURPS Russia book (here's an official excerpt), not for the rules, but for the wealth of info on the topic. Here's its blurb from its official page. (Note that it's an old publication. And its blurb is old as well, apparently. :))
GURPS Russia presents the Russian world from its beginnings in the
10th century to its new beginnings in the early 18th. In this book,
the GM will find complete details on the history, folklore, and daily
life not of the Soviet Union or of the Imperial Age, but of medieval
Russia – a culture that seems all but forgotten in the twentieth
century, overborne and overshadowed by the U.S.S.R. To most
Westerners, the word "Russia" is synonymous with communism, nuclear
war, competing space programs, and WWI-level farm equipment serving in
the fields of The People.
This book puts characters into the Russia of the Middle Ages, from the
10th century to the 18th. It also opens up the world of Russian
folklore and fairytales, where all sorts of interesting – and
sometimes frightening – creatures dwell.
Sure, you might want to go for a GURPS to D&D rules conversion solution as well. Then, if you've read GURPS Russia, all you have to do is come up with your own stats for creatures and people... or find their equivalents in D&D... or find them in D&D (though you might still need to do some conversion between editions), in which google will definitely help (here's a pointer for Baba Yaga, for example. And here's another. Both are official D&D.)