I would definitely try to get it, it covers your liability for accidents, etc. This is good, but moreover, many police will ask for it, and if you don't have it there is a good chance you'll have to pay a bribe or face some other problem (bike impounded, etc.). They also might ask for it at the border when you leave, although I'm not sure.
The Russian word for insurance is страхование, there are signs for it all over the place. Now that you are in the interior though, it might be harder to find somewhere that insures foreign bikes (not sure about this).