Mr Brown's former mistress and council ethnic adviser Bevan Chuang has joined the fight to save the garden, calling its demolition "disgusting" and asking "how we value friendship".
Late last year, the group lobbied Mr Brown and councillors to stop the garden being destroyed and to keep it intact at the zoo.
In a response on December 10, the mayor said he understood their concerns and was committed to retaining the "magnificent garden", but sided with the zoo which wanted the land to house a breeding programme for endangered Tasmanian devils.
No alternative site or funding has been found. The garden was established in 1989 as a joint sister city cultural project and opened by Auckland City Mayor Dame Cath Tizard, who backs the campaign to save it.
Fukuoka Mayor Soichiro Takashima wrote to Mr Brown on December 17 supporting the plan to relocate the garden and offering help. But after the furore over the demolition last week, Mr Brown has agreed to apologise to Mr Takashima and people in Auckland - possibly on Japan Day on February 23.
His office said the apology was "because despite the efforts made, local stakeholders felt they were not brought along in the process".
Stephanie Hay, head gardener at the zoo in 1989, said bonsai trees, rocks, the lanterns and entrance gate had been saved but estimated three-quarters of the garden had been destroyed. Group spokesman Roy Vaughan said members wanted to restore the garden and get an apology. People involved in the garden felt shabbily treated, he said.
Masa Sekikawa, the immediate past chairman of the Japanese Society of Auckland, said it was devastating to lose the garden but now it was gone he wanted to know why it happened, how it would be re-created and how soon.
The matter has been referred to the council-controlled organisation monitoring and parks committees for investigation. Mr Brown made a fresh promise yesterday to relocate the garden.
Garden mess
• Japanese Garden not wanted at Auckland Zoo
• Mayor Len Brown lobbied to keep it at zoo
• Brown sides with zoo and relocation to new site
• Garden friends outraged
• Brown to apologise to Fukuoka Mayor