These pieces[1][2] on the economy of soviet Poland say there was a black market of US Dollars:
> "the government, which controlled all official foreign trade, continued to maintain a highly artificial exchange rate with Western currencies. The exchange rate worsened distortions in the economy at all levels, resulting in a growing black market and the development of a shortage economy.[25] The only way for an individual to buy most Western goods was to use Western currencies, notably the U.S. dollar, which in effect became a parallel currency. However, it could not simply be exchanged at the official banks for Polish złotys, since the government exchange rate undervalued the dollar and placed heavy restrictions on the amount that could be exchanged, and so the only practical way to obtain it was from remittances or work outside the country. An entire illegal industry of street-corner money changers emerged as a result. The so-called Cinkciarze gave clients far better than official exchange rate and became wealthy from their opportunism albeit at the risk of punishment, usually diminished by the wide scale bribery of the Militia.[23]"
> "As Western currency came into the country from emigrant families and foreign workers, the government in turn attempted to gather it up by various means, most visibly by establishing a chain of state-run Pewex and Baltona stores in all Polish cities, where goods could only be bought with hard currency."
https://www.nytimes.com/1981/10/09/business/the-lure-of-a-do...
https://en.wikipedia.org/wiki/Polish_People%27s_Republic#Eco...