The only place I've ever seen aged Hibiki for sale is the tasting room at the Yamasaki distillery in between Osaka and Kyoto. The prices there are absurdly cheap though—$3 for a taster of the 17-year, $6 for the 21-year, and $29 for the 30-year. They also have a good selection of other whiskeys and scotches, including alternately-casked variants of Hibiki and their other whiskeys, also at low prices.
Here's a website with a pic of one page of their drink list, which looks accurate as of when I visited last year. It's a must-visit if you're in Japan.