Hi gblady. I'm going to China in May. Check out the Inspirational China thread for several other people also going.
You need worldwide cover for China, and I think Europe cover for Russia. The simplest thing to do, though probably not the cheapest, would be to buy cover from Just You when you book. Remember to declare any pre-existing medical conditions.
Personally I've purchased an Annual Worldwide policy through my employer's employee-benefits system. Being an annual policy it will also cover me if I decide to make another trip later in the year (which I may do, though not as long or as expensive as China).
Steve