Aloha shirts, also known as “Hawaiian shirts” is a shirt worn all over Hawaii. They first appeared in the 1930s and were originally made of silk and cotton. Their cut and style were largely inspired by the palaka work shirts work by sugar cane and pineapple plantation workers. When tourists flooded the new state of Hawaii from the mainland, the popularity of the Aloha shirt grew, along with the variety of the prints. While on the stuffy mainland the shirt is seen as excessively casual, Hawaiian natives wear these shirts in their day-to-day life. Nowadays they’re most commonly made with rayon and cotton, the perfect material for a hot day.
If you happen to live or know someone in the UK, you're in luck. My Nintendo Store in the UK is selling an official version of the shirt. My advice is to grab it while you can. They also sell kid's sizes, and even Isabelle's pink version. You can find these at My Nintendo Store in Japan as well (they also have a cool windbreaker).