Siberia is an extensive region constituting almost all of Nothern Asia. Conquered by Russia during 16th to 19th centuries, it makes up to 77% of Russia's territory, but has only 28% (40 million people) of Russia's population.
During the Civil War of 1918, Siberia declared independence, but was soon overrun by the Red forces, although there were pockets of resistance to the Bolsheviks until 1925.
From 1989 Siberian Nationalist organizations begin to grow again. Right now there are two main groups advocating autonomy or independence: National Alternative of Siberia and "Sibirska Vogota" (Siberian Freedom which is the link below flag).
Note that this flag has another version which you can find in this [link]