This might not be 100% correct, but from what I understand it was never on an app store, rather the phone was sold and distributed as is - an untraceable phone with apps preinstalled
Ok found my source:
> The Australian Federal Police then planted the devices with the pre-loaded AN0M into the hands of criminals by using several key criminal “influencers” – Australia’s Mafia Man, and Sydney fugitive Hakan Ayik, who is hiding out in Turkey.
> Sydney fugitive Hakan Ayik, who is hiding out in Turkey, was one of AN0M’s biggest spruikers to the criminal underworld. Sydney fugitive Hakan Ayik, who is hiding out in Turkey, was one of AN0M’s biggest spruikers to the criminal underworld. Police say Ayik and Mafia Man convinced their associates to use the devices, a move which gave police real-time access to every message, photograph or voice-message sent.
EDIT: Website https://www.anom.io/ (presumably the app has been taken off of app stores).