Not that close but Ashby do some nice rolling and can send the item mostly steel wheels for model traction engines, specticle plate folding, etc but should be no problem doing a smokebox, they do the wheels for MJ Engineering.
Probably have to come out of 5mm sheet but should be easy enough to adjust the chimney saddle or if there is a spacer ring between the boiler and box then get it rolled to the right OD.
J