Kubuntu should have the same packages as Ubuntu. If you can't find it in the package manager, drop to a console and do (as root) apt-get update (I don't know the guified paths in k/Ubuntu, sorry), then try again. If the madwifi package is not there, see if madwifi-source is. Install that, install module-assistant, and then again as root, try:
module-assistent a-i madwifi-source
This works on real Debian, should work the same on K/Ubuntu
Last way out, if the above fails: First you'll have to figure out which dev packages you have to install since K/Ubuntu comes with hardly any of the stuff you need to build stuff. You'll also need kernel-source or linux-source or something like that, for the version of your kernel, and linux-kbuild of the same version. Grab the daily snapshot from
http://snapshots.madwifi.org/madwifi-ng/ unpack, make, make install, depmod -a and you should be good to go.