Milne, 70, and his co-offender, Anthony Wayne Harris, 80, were both found guilty of various cultivation and supply offences at the end of a two-week jury trial in Greymouth in 2024.
Milne was jailed for six years for growing and selling 136kg of cannabis valued at $1million between January 2017 and September 2019.
His operation was based in an underground concrete bunker twice the size of the average New Zealand house, located at his accommodation business, Cowboy Paradise, at the top of the West Coast Wilderness Trail.
Harris was sentenced to five years in prison for his role in transporting and selling the cannabis in Christchurch.
He was found with $450,000 in his bank account when police arrested him.
The pair were successful in receiving lighter sentences in the Court of Appeal last year due to their advanced ages.
Each had their sentence reduced by eight months.
However, another attempt by Milne to further appeal his sentence in the Supreme Court has fallen flat.
The April 2 judgement outlined the offending and said Crown evidence at trial was that, on a conservative analysis, the underground growing operation could produce 136kg of cannabis annually with a retail value of $1.05m.
Milne was 68 when sentenced, had no relevant previous convictions and had a track record of contributing to his local community, the judgement said.
In the Court of Appeal, both men claimed their sentences were affected by a factual error concerning the seriousness of the offending — the sentencing judge had overstated the number of cannabis plants found at the property.
They also said the court was wrong to focus on the sophistication and scale of the grow — its potential yield — and should instead have given primacy to the number of plants found.
Additionally, they argued the starting point adopted by the judge was too high when compared with similar cases.
Finally, they argued that additional credit ought to have been provided for personal mitigating factors and in particular a delay of four and a-half years between charge and trial.
While it allowed the appeals, the court rejected the broader grounds.
Milne raised the same arguments in his application to the Supreme Court, but his leave for appeal was dismissed.
