Bob,
I offered to Brett, but it seems he is only at the planning stage, so ill offer it to you too, if youre a bit closer...
I have about 6m of single wall stainless flexi liner here (5" dia) that ive not been weighing in as i figure it must be useful. Its exactly the thing that you would want for a RMH flue.
I also have a load of night storage heater bricks, which would, i think, be ideal for the burn chamber...
Keen?