It's available here
ftp://rachelfriends.org/z-rachelandroid_APK/ However can I set your expectations as it might not work on some devices, particularly those running recent versions of Android from what I understand. If you have a device with Android JellyBean (i.e. versions 4.1, 4.2 or 4.3) it's likely to work with a bit of fiddling around to get it setup and the data files copied onto the device. From what I understand, this app was created with minimal funding to see whether it was possible to run a RACHEL server on Android, more of a proof of concept than a professional quality app.
It may be possible to develop a RACHEL for newer editions of Android especially if someone is willing and able to support the project either by creating the Android App or funding the work.
Good luck & please send an update on your progress.
Julian