Hansen has tried a number of players in the position since Kaino played the last of his 81 tests against the British and Irish Lions in 2017 but has yet to settle on a successor.
Liam Squire has been employed most often but struggled with injuries, Vaea Fifita and Shannon Frizell have also been trialled without convincing Hansen, and Akira Ioane has played once for the All Blacks against a French XV.
"We'd like to really establish someone in JK's (Kaino's) old role at six," Hansen told local radio station Newstalk ZB.
"Liam Squire's done a really good job there but he's been injured.
"We've got Shannon, we've got Vaea, and Akira's starting to play well for the Blues after a good season with Auckland.
"There's people putting their hand up, but they're probably not as established as we'd like going into a World Cup."
Squire, whose hopes of nailing down the number six jersey have been hit by a string of injuries in recent years, is yet to play a game for the Otago Highlanders in Super Rugby this season due to a troublesome hip.
He has already been ruled out of playing against the Melbourne Rebels away next week as the hip struggles to settle, while Fifita is working his way back to fitness after a hamstring injury.
Hansen said there was still time for unheralded players to break into the All Blacks squad for Japan, where they will bid to win the World Cup for an unprecedented third tournament in a row.
"This year, probably more than previous tournaments, there's room, because we've got some important decisions to make in certain positions, it's going to be about who puts their hands up and does it," he said.
"In a couple of positions we probably don't have as many (options) as we'd like."
He said his deliberations would continue deep into the Super Rugby season, which runs until the first week of July.
"We're looking for people who can show you, particularly in the business end of Super Rugby, that they can cope with the heat of the fire and the pressure that comes with it," he added.
"Because that's when the pressure is really on.
"But it's another level when you get to the All Blacks, you haven't just got your franchise looking at you, you've got the whole nation.
"For some, it can be overwhelming, and you've got to take the time with them so they can grow and learn to cope with it."
(Reporting by Ian Ransom in Melbourne; Editing by Nick Mulvenney)
