These are the Weber Summit grills and figuring out the exact model you have can be a bit tricky. The best way to tackle this is to pull the old Flavorizer bars out and count.
Seven individual Weber Flavorizer bars:
Two panels of Weber Flavorizer bars.
There are no aftermarket Flavorizer bars for these grills.
If your Summit is a model 2007 or newer and you want official Weber parts then you can contact Weber directly to order replacement Flavorizer bars (1-800-446-1071). According to a note from Tom in the comments section these are on back order.
The right part number is Weber 70375 and you can buy the stainless steel aftermarket Flavorizer bars for post 2007 Weber Summits from Amazon. These bars are 18.125 inches long and fit the Weber Summit S-420; S-440, S-450, S-460 and S-470. Here is the product link at Amazon…Stainless Flavorizer Bars 70375, Set of 4, (16 Ga.) Aftermarket