Kirk here. I saw something on RKK today about “COST MANIA,” a shop that specializes in selling (reselling) COSTCO items. Just opened in Arao, fairly far north for many of us but, if you’re in that part of the prefecture or passing through, it may be worth taking a look. Unlike COSTCO, you don’t need to be a member and they take things that COSTCO only sells in large quantities and sells them in smaller sizes / quantities.
https://www.instagram.com/p/C5xdrCGyWB7/
To find the location, pop the following address in Google maps:
〒864-0001 熊本県荒尾市原万田700−1
It’s behind the Yellow Hat (automotive shop) in the Anytime Fitness in the Ariake Plaza.