https://en.wikipedia.org/wiki/Soviet_invasion_of_Poland
And yet, my boutique academic journal Fuck Capitalism was rejected from Wikipedia’s list of reliable sources smh. /j 
Unfortunately I couldn’t find this article on Anna’s Archive.
Citation #9 is from Communist and Post-Communist Studies.
Oh wow, thanks! I thought Anna’s included LibGen, but I’m either wrong or bad at searching
I think it may take awhile for it to be mirrored but there is a download link for it via Anna’s Archive on the LibGen upload!