I think it's refered to as an outer ring or possibly a grate frame.
Try this link they might have what you are looking for. http://a1stoves.com/
Also I seem to remember some other plumbing supply place in PA that had parts also? Maybe someone can help. If worse comes to worst, You have that piece recast at Tomahawk foundry if you have the old one. If it's broken or cracked just JB Weld it back together and they can copy it. You get back exactly what you send so keep that in mind if you go that route.