I called Weber directly, mentioned #90720, and I was all set. The kind CS lady said they had them in stock, but didn't know how many of them. She said she thought they used to come on Performers and Mastertouchs, but I have only seen the one pair in the wild (on a plastic-table Performer).
I expect they will last longer than the 7444s, and also seem less likely to warp with high heat as I've seen the 7444s do. But mostly I like them because they are shiny. ;-)