FN 200100423 509 24rd 9mm Luger Black Steel
https://www.tandktactical.com/shop/845737011666-fn-200100423-509-24rd-9mm-luger-black-steel-29201
https://www.tandktactical.com/web/image/product.template/29201/image_1920?unique=4e1e7ef
This magazine is compatible with your FN 509.
