If it’s a 4″ vertcal then making one should be easy ! either from a lump of solid or sheet. I have a 6″ with the top made from copper sheet, though reeves do do a cast iron one – at a price ! Noel.
I purchased that casting last month and the quality seemed pretty good to me. It was the Kennions one. My only slight concern is that the chimney port is slightly less than a perfect circle, but its a casting not a forging. It will clean up fine. It’s got a nice radius to the top.