Came across these at Palmetto State Armory online:
http://palmettostatearmory.com/index.php/ar-15-05/ar-15-parts-sale/imi-defense-polymer-30rd-ar15-magazine.html
http://palmettostatearmory.com/index.php/ar-15-05/ar-15-parts-sale/imi-defense-polymer-30rd-ar15-magazine.html