Have you ever tried
Celga? It's a way of ordering things through Yahoo! Japan that are rarely found on our Ebay. 99% of sellers on Yahoo! Japan will not sell internationally but if you go through Celga, they will purchase the items for you and ship them to you. If you use a translator to search through Yahoo! Japan, I'm pretty sure that you will find Ayu concert shirts. They probably wouldn't even cost as much as they sell on Ebay sometimes. The cost of using Celga is a bit more than you might want to pay, but if it means getting a rare item, it's worth a shot. Good luck!
