The rib rack shown in the pictures on the Spare Ribs page is an older version Weber wire rib rack. The newer version has rounded ends rather than the squared off ends you see in the pictures, but is otherwise the same. They are commonly available where Weber products are sold, or can be ordered from Value America via the "Weber Store" link on the web site home page.
In the pictures on the Baby Back Ribs page, the old Weber Premium Rib Rack is shown, which was a really nice and well made 8 slot unit with removable slots and a porcelain frame. Unfortunately, it wasn't a very big seller and was discontinued. Fortunately, I had the foresight (luck?) to acquire two before their demise.
Regards,
Chris