Gluten free food in Poland is generally found in specialist stores, health food shops or delicatessens. In larger towns you will find some basics in the supermarkets, and mostly it will be in its own (very small) section. Piotr i Pawel has more then most, Alma usually has a few things, my local Intermarche has TONS, but you can usually find bits and bobs even in Carefour and Real and Auchan. As mentioned previously on this blog, tesco has nothing.
I live in a small town outside of Poznan, and even in this town there is a small delicatessen selling gluten free goods, and unlike other countries, it is NOT super expensive.