[elknise]

I know I live on the other side of the country, but at our Pacific Industrial Supply, i think i might have seen some larger than 7" by 7", but it is all steel and has walls at least .25 or .375.

I know out here we had to go to boeing surplus to get 3" by 5" aluminum tubing with .125 walls for a practice robot. Try a local surplus place, you never know what treasure you may find.