www.seat61.com is an excellent source of info regarding train travel. The LH side toolbar has "Russia" listed as one of the sources. It is excellent.

No one in their right mind takes a train to "save" money. Usually, airfare is cheaper. We take trains for an unforgettable experience. Such experiences cost both time and money - kinda like making/buying/drinking a nice wine versus some cheap "plonk".

I got my tix through waytorussia.com, and one of the firms that sell tix. Now to wait for the trip from Vladivostok to Moscow ;-)