I have in my garage right now five tubes at 12"I.D. and about 6` long which were made by a tube manufacturer just down the street from my business. I went in the front door and inquired about tubes that I saw sticking out of a dumpster next to the manufacturer, and they said that I could pick some up before they went to the dumpster if I wanted. They were free :) and I can get more ;)!!! They have from 6" up to about 24" in 2" intervals. They make a brand of sonotube which I can get them before they are treated with the wax or tar. They also make a really strong tube that has a wall thickness of about 1/2". This is the tube that I intend to use if I can ever track down an 11" mirror blank.

If you are intrested drop me a line at:
kight@valley-internet.net

PS. They make these tubes to roll paper on from one of our local paper mills. If the tube that is normally 20+` long has any defects at all they cut them in halves or quarters and send them to the dumpster.