Flexible exhaust tubing

I'm looking for a source of 1 1/2" flexible exhaust tubing. Mild steel is
acceptable. I want to use it for a model of the headers of a tuned exhaust
for my 0320 Lycoming engine that I have mounted in my Baby Belle helicopter.
The idea is to have 4 equal length pieces attached to exhaust flanges bolted
to the cylinders, arrange the 4 pieces to intercept the 4-into-1 collector,
coat the tubing with epoxy resin so that the shape is maintained and then
present these pieces to be copied by the exhaust bender.

Stu