I think the point was that the illegality was that manufacturers in the west was not supposed to sell computers to the east?

Illegal for whom? The manufacturers? It's the same as it's now illegal for Boeing and Airbus to sell parts to Russia, yet Russia developed a network of intermediaries in several countries that buy the parts on their behalf so they can maintain their planes. PEWEX stores used to sell of kinds of goods from the west, including computers and even cars, if you had the dollars it was far easier to buy a western car or a computer than wait for a domestically made one. Maintaining it afterwards was a different question of course, but PEWEX stores were created specifically by the government to obtain dollars, they bought goods in the west usually by barter, and then sold them domestically for dollars, which then they used to buy the goods they really wanted since no one would take Polish Zloty in the west, but dollars opened many doors.