It looks like an old one from a Spirit 500 or something but I would take a hard look - it may a pitted alum. pan covered in 5 coats of spray paint. I'd snatch that up in a heartbeat if NIB OEM and like 15-20 bucks
I have seen aluminum and on the last Silver A grills porcelain plated steel. There is little doubt that Weber never made one from stainless. I wish they did and especially for the larger three burner grills.