...final word I promise...

Magadan, Yakutsk, Skovorodino

The Atlas I recommended has
Magadan Oblast 1:4,000,000
Republic of Saka-Yakutia (Yakutsk) 1:6,000,000
Amurskaya Oblast (Skovorodino) 1:3,000,000

To do this journey, either all the rivers must be frozen OR for some of them you will need to find a friendly russian truck to take you across. Part of the journey is on a ferry. Ewan McGregor and Charlie Boorman did write a book and though the style is not to my taste, there is useful information. Probably best to flick through it in the bookshop.

Other maps I managed to obtain from the large bookshop in Moscow called...
Molodaya Gvardia
located very close to Metro Polianka (actually not far from the map factory I posted earlier)

Republic of Buryatia 1:1,000,000 printed 2003
Amurskaya Oblast 1:1,000,000 printed 1994
Chitinskaya Oblast 1:1,000,000 printed 2003
Khabarovski Krai 1:2,000,000 printed 1998

You could probably (almost certainly) find similar scale maps for Magadan Oblast and the Republic of Saka here.
Needless to say this shop is VERY well stocked with road atlases and maps of all russia, though the map factory ones were more expensive here - so buy direct from the map factory if you want 1:200,000 maps of anywhere east up to Tyumen.

Note that I have identified 4 map 'factories'. They no doubt produce larger scale maps in their locality which may not reach moscow, but if you are in that part of the world, it may pay to hunt about the shops / bookstands / kiosks a bit...

Moscow : Central Experimental War Map Factory
Omsk : Omsk Cartographic Factory
Chita : Zabaikalskoye Aerogeodesic Company
Khabarovsk : Far Eastern Aerogeodesic Company

Regards

Les