I don't have any really watertight first hand info unfortunately, only bits and pieces I stumbled over in German internet forums when I've been researching stuff for emulator coding.

Some of the stories of how Western machinery was procured is mentioned from time to time in articles like this one:

https://oiger.de/2011/08/26/die-teure-jagd-auf-den-megabit-c...

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.