Her Rarotonga-based sister Ellena, who is the head designer for Tav Pacific, had gifted the printed dress to Kate and a shirt to William but "didn't in her wildest dreams" expect the royal couple to wear them during an official function.
Ms Tavioni said she received orders from all over the world, and sold more than 200 of the "Kate dress", after pictures were published of the Duchess wearing it at a dinner with the Governor-General of the Solomon Islands.
The label has stores in the Cook Islands, Auckland and Honolulu and is retailing the dress, which comes in different colours including red and orange, for $325.
Ms Tavioni was hopeful that the royal tour could once again reignite interest in the dress Kate wore.
"When Kate wears something, everybody wants that something," Ms Tavioni said. "We're just proud to be able to say that we are the shop that dressed the royals."
Trelise Cooper, one of New Zealand's most successful designers, sent a nude and neon pink coat to London for the Duchess to try, but Kate has decided not to wear it and returned the coat.
This week, the Duchess was seen dashing into a Gap store in Kensington for some last-minute shopping for herself and 8-month-old Prince George.
British media reported she went with a nautical theme, buying two navy and white striped baby grows and a pair of striped grey and navy cotton trousers for George.
She also bought a green checked bodysuit designed to look like a shirt and some denim shorts, and grabbed two pairs of trousers for herself. It is thought by royal fashion watchers that Kate will choose to wear lightweight, comfortable materials such as cotton and silk to cope with the warmer New Zealand temperatures.
The Queen's personal stylist, Angela Kelly, has been engaged to help the Duchess prepare for the royal visit, where she is expected to wear up to four different outfits a day.
A Christchurch-made pearl brooch, presented to the Queen by Prime Minister John Key during his visit to Balmoral Castle last September, is among the accessories the Duchess is expected to wear.