I did a google search and Jackson and Perkins has an umbrella trellis. There may be more, but that was as far as I went. Of course no instructions there.

These aren't made from rebar...but are the actual umbrella frames. Hope this helps!

Here is a link that might be useful: Broken umbrellas

I know this is an old inquiry, but folks interested in garden structures should take a look at the links below. This is at the Getty museum in LA - well worth a visit for the gardens alone.

www.pbase.com/ robpavey/image/2181693
http://welchwrite.com/dewelch/photos/2003/gettygarden/pictures/DCP_3905.asp

I saw a neat one done with an old satellite dish turned upside down with post added.

Well, about the only positive thing that happened to me during Hurricane Wilma last year was that someone's satellite dish blew into my yard. I intend on doing exactly what taylo mentioned. Except, I will use three posts instead of one as I am anticipating more hurricanes this year. :)