Hello. Much to my surprise, I found a steel supply house in Livermore, Ca that sells to John Q. Public.
Here's a link to their site.
www.pleasantonsteel.com
I pickup up a 6' piece of 1 1/2 x 2 x 1/8" tube steel to beef up the tow car's
hitch for a bit more tongue weight capacity. Until I found this place I was limited to the big box stores.