Hi All
I have managed to stumble accross this website, with out making contact it would seem that I have found replacement cores and more for our circular core heaters, (SMITH)
http://www.claytoncc.co.uk/index.php?option=com_content&task=view&id=23&Itemid=37Smiths Replacements
Clayton manufacture a special range of the copper circular heat exchanger specifically to fit Smiths heaters on a replacement basis. Various versions and sizes are available to suit the various originals.
Motors, fans, and backplates are also available, as long as you have a serviceable front plate with doors, a new (improved!) heater can be built. For the purists this is virtually indistinguishable from the original (until you feel the heat when you turn it on
.)
Cheers Jim