Chinatowns always have Ayu. You just have to watch for bootleg and cheesey fake stuff. But a lot of times you can just tell.
I went to NY and looked at there Chinatown and in a separate Chinese Neighborhood and hit the jackpot.
most music shops will have their CDs divided by countries, gender, and genre
One shop in NY had Ayu on a shelf titled Japan:Female Artists
If nothing else, have her name in Kanji & Hiragana written down and give it to the vendor. I was lucky and had my Chinese friend with me, so he did the talking. But search on your own. Try all the stores that sell music & Anime. Going to New York was like visiting a mini-Japan. The chinese know that there is a good market in anime and japanese music, so they invest.
Most of the bootlegs are obvious. They'll have random Ayu pictures as CD covers or will have the wrong title. hehehe some of them are just hilarious. So you can usually tell what's real and what's not. As long as you are knowledgeable.