I cannot find a 2.4 version of the debian installer... could anyone point me in the right direction?

There is no installer at all (because none is needed ).
Maybe you are referring to the .deb packages. These might take a while to get updated in the repositories depending on the distribution you are using.
If you want to run Nexuiz 2.4 just download the zip file from http://alientrap.org/nexuiz/downloads.php and extract it anywhere in your home directory.
Than start one of nexuiz-linux-glx.sh or nexuiz-linux-sdl.sh in the Nexuiz directory you extracted from that zip file.