There is a fairy tale going around that "a lot" of polish people are buying cars here and ship them to Poland
There was a report on the BBC, a week or two ago, about Americans selling their cars because of the rise in fuel prices. The report focused on SUVs
Anyone selling an SUV at a significant loss would possibly make it the Polish guy's gain.
From what was suggested on the news, there might be some truth in the story, and profit, for the enterprising Pole.
There are people who imported cars from Germany. Maybe they have seen an opening in the states.
And, what are the most popular websites for buying/selling cars
The most popular paper would be Auto Giełda. So you could try their website.