They did commentary on "The Day the Earth Froze", which is an edited version of the Soviet-Finnish film "Sampo" loosely based on the Kalevala.
See it yourself, at https://youtu.be/yRhXcxx1SwM?t=958 .
But yeah, the Russian movies from MST3K were some of my series favorites.
And I still don’t know what the Sampo is!
No one does. Sampo is basically just a magical MacGuffin that brings wealth to whoever has it. In Kalevala it is usually understood as a mill that creates infinite grain, salt and money, but different folk stories have different interpretations.
You are not alone! Scholars are still debating it. It is some kind of magical device which create wealth, but there is a number of very different theories raging from a magical mill to the "pillar of the world".
(Edit: it's possible it was Sampo, even though that seems to be in color. We just didn't have color TVs back then).