A good castor bean mail-order source is the following:

Wuv'n Acres Gardens: Unique, Unusual, and Often Hard-to-Find Garden Seeds
http://www.wuvie.net
E-mail: Karen@wuvie.net
Address: Roger & Karen Manasco
14280 North Sunset Valley Road
Hulbert, OK 74441-2052
(918) 931-9688

You might also, just wait and see if you get any volunteers. I had a few plants years ago and remember pulling up a lot of babies the following year (or two?).

I can send you some. Castor grows wild here. We always used it as a shade plant or wind barrier. I think I even have some that I collected down by the Indian River last year...
I don't think they've set seed yet...(gives me a goooood reason to ride my bike out to the Lone Cabbage and check though!