This is quite easy, actually. If you are working with GNU Ispell, you
just need
Russian dictionary
originally made by Neal Dalton in 1992 who gave it up eventually. The
dictionary had only 50 000 words which is basically nothing. However,
Alexander Lebedev (swan@mch.chem.msu.su) picked it up and now it has
over 420 000 words. His edition was buit using the Orthografic Dictionary
by the Institute of Russian Language of the Russian Academy of Sciences.
The riginal FTP site where the dictionary is located is at
mch5.chem.msu.su.
If you are under some kind of Windows/Mac, as far as I know, there are no
freeware dictionaries (unless you managed to find some pirate copy).
Refer to Russian edition of MS Word, for example.