Im afraid the control knob you are looking for is now obsolete. Ive checked all the parts site i use and none of them show it as in stock.
As most spares site work the same. When you order a part they get it direct from the manufacturers. As they dont make them anymore none of the spares site sell them anymore.
The part number if you need it is C00238293.
But i suggest you can try is take one of the old knobs off and go to your local spares shop. If you look in the yellow pages you will find it. And see if they can match one up for you. As some do verisous knobs which may do the trick and get it so you can use it.
Sorry its not good news but if you need anymore info just get back to me.