Chicago Tube and Iron. There are at least two in MN....St. Paul and Duluth. There's also an office in Owatonna.
Ron , how much do you need? i have a bunch of it borrowed from where we used to work..probably 20-25 feet. i also have it cut to length for 4-bar ends
I have bought from All Metals Inc and Speedy Metals. I was really surprised with the shipping cost, very reasonable. They will cut the material to your specified length.