I got those particular shelves at ACE Hardware. They are the 48 inch wide ones and are black in color. They also were on sale! I think you can get wire rack shelves just about everywhere. These hold 350 pounds per shelf.

After putting some tanks on the rack I decided to cut and fit some MDF sheets to fit inside the wire rack perimeter and corner posts. This allowed the shelves to sit better and certainly makes it much easier to slide the tanks on and off if needed.