Several thousand ex-military guns could be in the hands of civilians, the Defence Force says.
Two weapons found in the house of Napier gunman Jan Molenaar were standard army issue, the Defence Force has confirmed.
Mr Molenaar, 51, shot one police officer dead and seriously wounded two others and a civilian in May this year, before barricading himself inside his house.
He was found dead two days later.
A police search of the house found an arsenal of 18 firearms along with fully loaded magazines, more than 100 spent cartridges, 2000 bullets and improvised explosive devices.
Police say three of the guns had been stolen and that Mr Molenaar's firearms licence expired in 2002.
A Defence Force spokesperson says two self-loading rifles (SLRs) found in Mr Molenaar's house were issued to members of the army beginning in the 1960s but were sold off in the 1980s.
Commander Shaun Fogarty says members of the public could buy SLRs after they were replaced by a more modern rifle.
Commander Fogarty says says records do not show exactly who bought the guns, but there could be several thousand in the community.
He says the siege in Napier proves weapons that end up in the wrong hands can have terrible consequences.
The Army is to install microchips in all its firearms to keep an accurate track of where they are.
Police National Manager of Firearms Licencing and Vetting, Inspector Joe Green, says it is not common for military weapons to end up in the wrong hands