"They flew from Australia with that letterbox in baggage," Karen said.
"They carried it around the North Island on their holiday before they brought it to our house.
"The joke is that the colours for John Deere are green and gold, which are the colours for Australia. He put an Australian-coloured letterbox outside our door."
The tractor weighed about 15kg and was made of recycled gas bottles by Australian man Peter Demartini.
Karen said the mailbox was really special.
"Roger came over for my 50th birthday in March. On the day, we got a phone call from the Australian Police saying that Peter had committed suicide.
"It was really tragic."
Peter lived in Townsville, where he worked in the mines and was Roger's close friend.
Karen had known him for about 20 years. The Lithgow's road had been targeted prior to the mailbox being stolen.
Tractor Pete had been sitting on a plinth with two neighbours' mailboxes, and one morning they discovered all of them on the ground along with nearby road signs.
A neighbour across the road told the Lithgows he thought someone might pinch their beloved mailbox, so helped them bolt it to the plinth.
"They came back the next weekend and stole the whole lot," Lithgow said. "These lads must have used sledgehammers to knock the whole plinth off.
"These hooligans have taken what they think is just a letterbox, but it is actually something that means a lot to us." A police spokesperson confirmed they received three reports of stolen mailboxes from Western Line addresses over September 8 and 9.
There were no immediate lines of inquiry and police would like to hear from anyone who has any information about the thefts.
Anyone with information should call 105 and quote the file number 190909/5104.