Source and some binaries are on github :
https://github.com/gbarrand/pmx.git
pmx is available on the AppStore since January 2012.
pmx is available on the Android Market for devices with at least Android-2.0.
On a Mac, download and unzip the pmx.app.zip, then click on the pmx icon (or do : open pmx.app, from a terminal). Remember that data files are searched within the directory :
~/Documents/pmx