OK, maybe I've been poking around too many Russian sites these days. Admittedly though, it's great seeing a massive reenactor community that we don't often keep our eyes on. From the photos posted on the various sites, they have a community to take careful note of.
So this fringe is dedicated to the Russian Civil War, the conflict between the Red and White Russian armies. This would also have interest with American, French, Canadian and British WW1 reenactors, since both countries sent expeditionary forces in support of the Whites as part of the Allied Intervention. Lots of interesting things happening in history at that time.
The only Russian Civil War group I could find is Empire, which also covers WW1 and WW2 reenacting also. On the Russian Civil War side of things, they seem to do mostly living histories. There seems to be a fair representaion of both sides of the conflict, but they don't have any of the intervention forces represented. But hey, they seem to have their hands full with the primary armies. This is a great site to surf, and you'll learn a thing or two about Russia in the early 20th century.
Another reenactor resource that includes the Russian Civil War is the EastFront Yahoo! Group.