You are talking about rolling three parallel helixes here. I have had problems in the past just getting 8" Sch 80 316SS pipe rolled that way for an AESS spiral stairway in a residence. Unless it is a very large radius and low slope, (like a sweep you might find in a parking garage ramp,) I would recommend getting a change order so that you can use fabricated members.
Joe Kane
Scott,
I know we are on opposite sides of the country, but, you could also try:
Arbogast Construction, Inc; Fort Mohave, AZ
1 (928) 788-2653
acirolling@frontiernet.net
Ask for Kevin. They are about the biggest in AZ and most of the West Coast. They have done some pretty good sized pieces for me but those are even bigger. They have also done rectangular tubing for me in a helical for a spiral as you are asking for. They were so very close from my measurements that it took almost no tweaking to get it done.
Have a Great Day, Brent