The British Ironwork Centre in Aston, near Oswestry, which is behind the project, began supplying knife banks to the 43 police forces across England and Wales two years ago, with the backing of the Home Office, and since then more than 100,000 knives have been taken off the streets.
But only 37 police forces have contributed.
Dyfed-Powys Police, Gwent, South Wales, Lincolnshire, Sussex and South Yorkshire are yet to send the centre any knives, leaving the project at a standstill.
It was hoped the sculpture would go on display on the fourth plinth at Trafalgar Square, but Clive Knowles, chairman of the centre, has refused to unveil it until the remaining forces have sent in knives.
He said: "We can't even try and take the sculpture out of the studio until we get the remaining forces to action their surrender amnesty.
Originally we pledged to get 100,000 knives off the streets with the backing of all 43 forces. It's been created against and to raise awareness of Britain's issues with violent knife crime, so we're not able to unveil it until all constabularies are on board with it."
Mr Knowles said his particular issue with the lack of support is that it comes at a time when the latest figures on knife crime show a nine per cent rise nationally.
He said: "How can police forces not support this at a time when the crime is on the up, especially when a company is willing to support and fund the bins and banks. "If a fatal stabbing happens in one of these forces areas, how will a chief constable explain to families that they failed to hold an amnesty that was being funded already? That will be a very difficult conversation.
"We can't rest now, not this close to the finish line. The project will never fulfil its destiny if this doesn't happen."
The aim of the statue, created by sculptor Alfie Bradley, aims to raise countrywide awareness of Britain's knife crime epidemic with its 'Save a Life, Surrender Your Knife' slogan.
Families affected by knife crime have also had the names of loved ones inscribed on a knife in the angel.
Dyfed-Powys Police were unavailable for comment. South Yorkshire and Gwent Police said they were unaware of the project.