Honestly, if you can go somewhere with a Chinatown, the chances increase A LOT, but as a US citizen and rabid Ayu fan...it's near impossible...
I'm going to Uwajimaya in Seattle WA, USA in a few days. There's a bookstore called Kinokuniya that has tons of Jpop CDs and DVDs!!!
KINOKUNIYA bookstores, remember that!
I bought some Ayu CDs and DVDs from there in the New York branch. Google it and there are a few locations!