There are many places that you can buy Christmas ornaments in Warsaw. And the ornaments that they offer vary in price and they are from many different manufacturers.
Bracelets, Pendants, Necklaces
Pierogi & Ravioli Forms
Pierogi & Ravioli Recipes
Railroad Model Supplies
One can generally be assured that they are the typical high quality Polish ornaments.
There are no shops in Warsaw that specialize in Christmas ornaments. You can find Christmas ornaments in the shops that sell souvenirs.
Such shops are generally located around the Warsaw Old Town.