It was unlikely the issue would come before the council "this side of Christmas", he said.
In June, Mr Cairns suggested the regional council consider moving into the former chief post office building alongside the Dunedin City Council's libraries.
This week, the city council revealed much of the homework had been done by consultants on a redevelopment plan for the historic building.
City council property manager Robert Clark also said reasonably serious interest had been expressed in the two other floors, but would not say from whom.
Mr Cairns said the interested party "could not be" the regional council.
The regional council had removed funding for new premises from its long-term council community plan and, in June, agreed to reconsider all options.
"We're back in the re-deliberation process, but it has not advanced too far."
Councillors had held a workshop on the issue and would be "coming back together" to re-examine its original vision and scope for new premises.
"Once we've done that, then we move into looking at options."
The issue would not come in front of the council before Christmas, and he was "not sure" when it would in the new year.
