Sounds like a fun VBS! I used to be a Children's Ministry Director, so I've done a few VBS' (like, 12 or so!). Blessings on your planning and organizing - hope it all goes well for you.
What kinds of symbols are you using for the other countries? Are you using flags or animals or something? I'd think that even just using the flags or outlines of the countries would be something the majority of the kids would grasp. How young are you going? 4's and up should be able to grasp those as symbols.
For Poland there's always the Polish flag - and there's an eagle design used as the national seal as well. If I remember correctly, fishing is a large part of the culture, and I've seen some designs that incorporate a fish into a symbol for the country.
I'm trying to find the pictures of my Polish friend, Marya, in her "traditional" dress, but I can't locate it yet. I do know that the colors red and white are very important and have many symbols. Right now a lot of the postcards, etc. I've been getting from Poland have pictures of the previous pope as they are very proud that he was from Poland.
Try doing a Google Image search for "Poland" and see what you find.
Good luck!