For the past four or five years, one of his 105mm Pack Howitzers has been borrowed for Anzac Day services in Dunedin.
As the owner of an extensive military collection, he has become used to getting a phone call from the army "or a Unimog turns up occasionally to load things on".
"A lot of stuff I've got, you just can't get it," he said.
Mr Dempster, who is in his late 60s, has been collecting "bits of military stuff" for years.
It started with small items and "just sort of grew from there".
The comprehensive collection includes firearms, artillery, vehicles and all manner of other military-related items.
He was only aware of three 105mm Pack Howitzers in private ownership and he owned two of those.
"A lot of people say, 'where do you keep all this stuff? 'I say, 'just under the bed'," he said, laughing.
Sourcing items was a challenge but they often turned up in unexpected places.
"Everything's out there. You've just got to find it.
"When you're driving around the country, you keep your eyes open. You might see something under a hedge. That's what it's all about [collecting]; finding that spare part."
Mr Dempster is a member of the 44 South Military Collectors Club and he and his fellow collectors all looked out for each other. The group sometimes staged displays, including at Warbirds Over Wanaka.
Among his vehicle collection were three Mutts (military unit tactical trucks) and Mr Dempster believed there were only about three others in New Zealand.
In England, Mutts were selling for about 30,000 ($NZ62,000) but he did not know what the New Zealand market was.
He was not tempted to sell any of his collection as he considered his hobby was helping preserve history.
"If you don't save it, it's gone. Too much stuff has gone out of this country," he said.
War veterans enjoyed looking at his collection and he tried to "keep things right, as they would have had it".
