Hi Rodger;
I haven't heard of anyone making flue liners for RMH's.
But I don't see why you couldn't.
They would not work in the riser, but would be just fine as piping thru a mass.
If you have the time and materials it sounds like a fun project.
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It would depend on the use for the flue liner, and the character of the local clay. If you are looking for RMH channels in a mass, yes, it would be perfectly feasible. If you are looking for a chimney for a wood stove, that requires particular thermal and chemical properties which most native clays would probably not possess without correct additions and modification.
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