Check out the nukes module, not just the nukes directory in CVS. This will get you the thirdparty and tools modules as well - that's what you are missing.
I think that's what i've done. I got the source (and the libs) from cvs by the commandline on the page.
cvs -d :pserver:email@example.com:/cvsroot/jboss co nukes
I have the tools directory with the ant stuff and the thirdparty dir with JavaCC.zip. I get the same problem if download the source zip from the page and try to compile that way.
It feels to me like there's a command definition missing from the ant system somewhere, since i got the jar/zip for javacc.
It does look like you have everything you need. I would try running the build script with Ant debug and verbose options on and see whether anything strange is happening - you can pass the flags as parameters to the build.sh.
I found the problem which was that i had ant installed from jpackage wich overrode the ant in the nukes buildsystem. :-/