I was recently browsing www.highend3d.com when I came across a script that exports from blender to the renderman RIB format. I tried it but it doesn’t seem to work under Blender Publisher and most probably any newer versions.
You are wrong stop now!! Well, you are not wrong but you also have an option: Jan Walters himself is writing a new RIB exporter. You can follow his progress here. I would also suggest you to check this thread over at http://www.blender.org, because he seems to be seeking help, you may want to give him a hand (hint hint ;))