If you are on mobile, there will be 3 bars in a brown square box in the top left of your screen. Tap that, and a blue box will appear. Under "home", it will say "forums" Simply select that. It will take you to a page with a list of everything, scroll through there and find "buy, sell, trade" or...
Try checking out the "Buy~Sell~Trade" part of the forum, or you can search "polish thread" in "general breed discussion and FAQ" and ask people on the polish thread where to get them.