Weapons regularly fall into criminals' hands because there is no effective way of tracing them, British charities say.
The gun used to kill Pc Broadhurst was part of a batch from Croatia
Countries cannot be held to account for weapon exports because there is no international record of serial numbers, Control Arms campaigners claim.
They want the UN to adopt a legally binding system to mark and trace small arms, light weapons and ammunition.
"The British government must use its influence to push for urgent change," says Oxfam's Anna Macdonald.
"It is outrageous that you have more chance of tracking a GM tomato or a suitcase than you do an AK47 or rocket launcher.
'Disappear without trace'
"A piece of lost luggage can be tracked from London to Liberia within hours, yet deadly weapons disappear without trace on a daily basis."
The campaign, made up of several charities including Oxfam and Amnesty International, brought out its report to coincide with a UN conference on marking and tracing in New York.
It highlighted the murder of Pc Ian Broadhurst, who was shot dead in Leeds on Boxing Day 2003.
He was killed with a gun which was one of more than 2,000 weapons licensed for export from Croatia, using false paperwork and front companies in the US, British Virgin Islands and Nigeria, it found.
Spent cartridges found after 150 people were killed in Gatumba, Burundi, showed they were made in China, Bulgaria and Serbia, the report said.
But because there was no proper way to trace them, there was no way to prove how they got there, the Control Arms campaign said.
In September, Foreign Secretary Jack Straw said Britain would support the campaign for an international treaty to control the arms trade.