In Jersey City there's one downtown. It's called I think Europa and the address is 527 Jersey Ave. you can buy different kinds of Polish meat, sausage, cheese, candy, bread, cakes and p±czki :D And there's a Polish travel agency like across the street.
You can also buy Polish cookies, marinated mushrooms, & other Polish products at A&P's around here.
There's also a Polish Deli called Sawa, also in Jersey City, I think it's on Central Avenue, near Dickinson HS
And in terms of shops outside of NJ (but near Jersey City) well, you can always go to the Greenpoint area in Brooklyn, it's a big Polish community, full of Polish stores and restaurants. Or, go to Brighton Beach, also in Brooklyn. It's mostly a Russian community but you can often find products like Polish juices and water (Nałęczowianka, etc.) in the stores. Plus you can enjoy a day at the beach and/or Coney Island while you're there 8)
Hope this helps people.