As I thought, some of these papers can be downloaded from Russian sites, although sometimes as a full journal or issue rather than as an individual article.
One possible complication is that Russian websites often post documents in DjVu format rather than pdf. You will need to download a reader, which should be available for free. You click through the pages from the bar at the top. You can also convert DjVu to pdf (although I have not tried it).
The Archive for the Russian journal Priroda in DjVu is posted here:
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The Geokniga website is a bit tricky to work through, but here is a link to some of the publications (in DjVu) by Efremov:
You need to click on the title, then go to the bottom of the individual page for the publication and click on the link.
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Chudinov's book on early therapsids from 1983 is here:
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I may be able to get links for some of the other papers, but it can take some time to get the queries right in Russian, and, of course, some papers may not be online at the moment.