In this thread http://weberkettleclub.com/forums/index.php?topic=36353.msg367125#msg367125 , @Bob BQ mentions you can use a cast iron grate from a Genesis Silver B or C. And, in this thread http://weberkettleclub.com/forums/index.php?topic=28777.msg284314#msg284314 , ECinEI mentions having a Weber griddle that fits in half the grate area of a Genesis Silver, so that gets you there except for a part number.