Polish currency can be ordered from UK and other banks before you arrive. If you do not bring any with you, you are advised to change only sufficient currency at the airport to cover your transport costs to your accommodation, as the exchange rate at the airport is considerably higher than at exchange points in the city.
You can also find exchange points in the centre of Gdańsk. The nearest one is in the Madison Shopping Gallery.
More information about the gallery you can find at: http://www.globalblue.com/destinations/poland/gdasks-madison-shopping-gallery/