Do you mean flats depicting Russian subjects, or flats made in Russia? I'm not sure there are very many of the latter, if there are any. The flat originated in Germany, and though there have been makers in other countries, the overwhelming majority of makers are still German. However, many of those makers have Russian subjects, like Napoleonic soldiers, Cossacks, 18th century, in their catalogs.
There are Russian toy soldiers from the Soviet period, produced in a half-round style. They're distinct from the German half-round figures (eg, Ideal or Schneider) in the style of the sculpting, but still toy-like. I have a set of Russian sailors in this style.
Prost!
Brad