Seasons/Availability
Hyuganatsu citrus is only available for a few weeks in the early to late spring when cultivated in outside orchards. The citrus is also grown on a small scale in greenhouses, producing fruits from the mid-winter to the early spring.
Today Hyuganatsu citrus is primarily grown in the Miyazaki Prefecture and is found through specialty distributors, roadside stands, and local markets. The citrus is also grown in other regions of Japan under the names Konatsu and Tosakonatsu
Info from Specialty Producehttps://specialtyproduce.com/produce/Hyuganatsu_Citrus_15764.php
Not sure if you could track down a fruit if you visit Japan ? Might still be available from coolroom storage ?