You say you've got a few lenses laying around and you don't want to use plastic tubing and aluminum tubing in the sizes you need are just to hard to come by. Is that whats troubling you, Bunkie? Well just march yourself to nearest truck parts store. (large trucks) They have exhuast pipe in 3, 4, 5, and 6" diameters up to 10' long. Show the world, never give up! 
Seriosly, guys I did just that on a "why not I just might get lucky " and came away with 4" and 6" pipes. They need cleaning but they are round, straight and strong
Seriosly, guys I did just that on a "why not I just might get lucky " and came away with 4" and 6" pipes. They need cleaning but they are round, straight and strong
