FN 20100261 503 8rd 9mm Luger Stainless/Black
https://www.tandktactical.com/shop/845737009090-fn-20100261-503-8rd-9mm-luger-stainless-black-23520
https://www.tandktactical.com/web/image/product.template/23520/image_1920?unique=f0d95ec
This magazine is compatible with your FN 503. It features a stainless steel body with a black base pad.
