Joe, Great big project you have going there.
Here is a web site for a stainless steel flex tubing. It appears to have the characteristics necessary for your project, but I am not endorsing it. I just found it and have not researched it thoroughly. That will be up to you. I also like the way the tube is made. There are no seams. I however do not know what the minimum bend radius is nor how many times the tube can be cycled through the bending. This is a start for your search. Contact them and see if they can help you get what you need.
Look at the corrugated hose by Penflex. I called them and their product has been used in exhaust applications. Use their engineering staff to help you determine which product is best. Have them recommend a destributor that would sell you a small quantity by the foot. You can see some of the specifics by downloading their PDF catalog. This looks better than the first tube which I erased.
http://www.penflex.com/
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