Arch Linux
There's a rolling AUR package called pam_panic-git and for tagged versions called pam_panic.
Ubuntu
There's a PPA.
To install the package using the PPA:
sudo add-apt-repository ppa:bandie/pampanic
sudo apt-get update
sudo apt-get install pampanic
Compiling from sources
You will need GCC or similar, as well as the PAM headers. Some distributions package the PAM headers as libpam0g-dev.
Also you need po4a and gettext.
To compile and install it, do the following within the project's root directory:
$ [ ! -e ./configure ] && autoreconf -i
$ ./configure
$ make
$ sudo make install
Note: the paths of the reboot, poweroff, and cryptsetup commands are passed to the module at compile-time.