He said he felt driven to do it because every month he was reading the obituaries of the heroes of World War II, and he realised that there were just three remaining Dambusters from the 144 who took off on May 16 and 17, 1943.
Fifty-three airmen perished in the raid, with only 11 of the 19 bombers getting home.
"As a portrait painter, I felt I owed it to their memory to paint their portraits ... documenting the quiet, modest heroism is a passion of mine."
Despite his determination, which included doing the work without a commission, Stone did not like his chances of securing permission from the three men, anticipating their reluctance to be glorified.
However, with a bit of gentle persuasion he broke down their resistance and was now into the process of painting the second portrait - Mr Munro.
The first subject was Bristol-based veteran and Squadron Leader Johnny Johnson and the trio will be completed when he paints Canadian Flight Sergeant Fred Sutherland.
"The best bit of all was the chance to get to know each man."
Stone said he started sketching Mr Munro within two hours of his arrival in Tauranga last Sunday.
He operates informally by "splashing a bit of paint" on what will become a sketch while sitting next to his subject chatting.
The sketch became the basis for a full-sized head and shoulders portrait, which he painted in his studio in England.
Both men are enjoying the bonds that have built up between them this week, with Stone saying a lot of portrait painting was intuition and understanding the personality and spirit of the person.
"I have enjoyed every second of this man's company and, when I leave on Sunday, I feel I would have made a new friend."
Mr Munro said that 71 years ago he would have been hard at work with the crew of his Lancaster bomber practising low-level flying and bombing techniques for the 617 Squadron's attack on the German dams.
But despite the months of training, Mr Munro was denied the chance to deliver his bomb when the plane's communication system was destroyed by flak along the Dutch coast and he was forced back to base.
"I can't be part of the glory of that successful raid, that is the downside I feel," he said.
However, Mr Munro's war was far from over and he went on to distinguish himself on a number of other missions.
These included flying ahead of Lancaster formations to act as a bombing co-ordinator, dropping aluminium chaff on D-Day to fool German radar and leading the mission that knocked out German U-boat pens at Le Havre.
The three paintings will be displayed by the Imperial War Museum although their final homes depend on the wishes of the veterans.
Mr Munro is considering putting his portrait into the Wigram Air Force Museum or Te Papa and, in the meantime, he will receive prints of his portrait once it is completed.
The British High Commissioner to New Zealand, Vicki Treadell, said it was an opportunity for one of Britain's greatest portrait artists to capture in a unique way the remaining few World War II veterans who did such courageous things in defence of freedom.
