"We thought people would be more likely to make an effort to look with a high reward - and the more eyes on him, the better," she said.
Mr Miller, who with his wife manages Scott Miller Motors at Solway, said Herbie went missing from their backyard on November 2. "I tripped over, and he just slipped out of my hands and went straight over the fence," he said.
He said this behaviour was out-of-character for the docile Herbie, who was usually happy to hang out with his "parents" on the couch, sharing their dinner and Milo.
"When we got him, he'd try and attack us every time we walked past - but we got to the point where we could pick him up and hold him. He'd sit on our shoulders and on our heads, and spend every night on the couch with us."
The Millers put up posters of Herbie around Carterton, and several people have reported seeing him but none of the leads have panned out.
Some people on the lookout are even playing downloaded cockatoo mating calls out of windows.
"People have told us 'we don't want your money, but we're really watching out for him'," said Mr Miller.
The Millers advise anyone who sees Herbie in their backyard to tempt him with food - especially corn chips and tortillas. Do not let children approach him as he is terrified of them, and will fly off.
The couple hope Herbie will "get sick of eating pine cones" and come home for dinner and Milo. "I miss him, I really do," said Mr Miller.
If you see Herbie, please contact Scott or Kathryn Miller on 06 379 9254 (home), 06 370 1641 (work), or either 029 773 0734 or 027 226 8699.