According to New Scientist, Raytheon, the defense contractor behind the pain gun, is working on a portable version:
Raytheon is now building smaller versions for law enforcement or commercial maritime use – designed to be placed inside buildings, such as prisons, or mounted on ships for defence against, say, pirates. And soon there could be handheld versions of the pain ray. Raytheon has developed small experimental prototypes, one of which is about the size of a heavy rifle and is intended for police use.