aww! I live in San Diego now but I spent the first 3 decades of my life in the Chicagoland area and used to work just down the street from Helen’s. We’d go there for lunch periodically and it was always an experience. Great pierogi! Kinda strange just seeing it pop up in a random thread I clicked on 
True oscypek would have to be imported. I prefer serki góralskie, which is extremely similar, and can be made locally.
… and where do you buy it?
I still have not been able to secure any of this cheese (I just looked for some today, in fact) but I did find this nifty 3 minute video on how oscypek is made.
I came across this thread of someone looking for oscypek near London:
I’ve been out to the Polish Deli twice in the last year but zero times since the start of the pandemic; still no luck.
I love the super helpful replies in some of the comments on that Reddit thread: “Try asking some European or Polish shops!” Thanks, Captain Obvious.
That said, some of the comments were kinda cool. I didn’t realize there’s such a close analogue in both Czech and Slovak cuisines, although that makes sense.
May the fleas of a thousand camels infest the armpits of whoever on Reddit up there suggested smoked Gouda as a similar substitute, though. That’s like ordering a Jack-and-coke and being handed an iced tea.