Sera-Myu Store

eternal.legend @ Cafe Press - Show your myu fandom with these shirts, buttons, stickers, and more. Designed by Taka.

YesAsia.com - Pretty decent selection. Site is completely in English and they have really cheap shipping.

Amazon.co.jp - HUGE selection. Site itself is in Japanese, but ordering information is available in English.

Amazon.com - Considering it's a US-based site, they have a really good selection!