I had replied to this before the crash. There are two prestige classes I think you would like.
The first is from Frostburn, and it is called Winterhaunt of Iborighu. You would probably be Chaotic Neutral if you went this route. They desire to make the whole world into an icy domain like their homeland, and follow a Frost diety. They have full divine spellcasting progression, and various cold powers. The picture even shows them holding a wicked looking sickle, and the class has a russian feel to it.
The second is from the Book of Exalted Deeds, and is called Sentinel of Bharrai. Your alignment would need to be "any Good" for this route. They are a nature-oriented class that worships the "Great Bear". They have full divine spellcasting progression, and various bear-related powers and nature-related powers (though not like a Druid, more like a Ranger).
Hope that helps. I have some of the modules from the Russian-themed setting that one of the third party d20 writers came out with, so I will see if I can find anything with that. I've been meaning to get Frost and Fur: The Explorer's Guide to the Frozen Lands. That probably has some more good Russian-themed prestige classes as well. If you have any interest in seeing their products, here is a link:
http://www.rpgnow.com/product_info.php?products_id=5773
From Frost and Fur: The Volkov (pagan priests) class, vedma (witch) prestige class, vorozhei (fortune teller) prestige class, and znakhar (healer) prestige class, might be up your alley (I have not seen it yet so I don't know).