Not sure about the Soviet Union, but East Germany had to "import" complete production lines from Western Germany in order to bootstrap their chip production. Of course the West prohibited exporting such sensible technology to the East, and there's some wild stories around involving the secret service, setting up a proxy chip manufacturing company in Western Germany, shutting this down, and "losing" the production lines, which showed up a few months later in East Germany.
But there will be plenty of Z80 and other 8-bit chips to scavenge after a civilizational collapse, and those chips are simple and slow enough to be used in computers built from breadboards and wires.
Some of the stories of how Western machinery was procured is mentioned from time to time in articles like this one:
It seems to have been less "broad sweep style" than I mentioned above though, more like that new products required specialized machines which were only produced by a handful Western manufacturers, and which were under the CoCom embargo. And the "grey-importing" of those machines went through various shadow companies in different countries to cover everything up.