They are literally everywhere dude! I'm sure you will find them in any big computer/elecronic market. According to www.pconline.com.cn creative HN-505 is around 399RMB so it should be around that price (keep in mind). I would go to Pacific Digital Plaza (Tai Ping Yang Shu Ma Guang Chang) on 117 Zhaojiabang Lu (near Caoxi Bei Lu) in Xu Jia Hui. Open 10am-8pm and they accept international credit cards.
Noise canceling head phones range from 150RMB-3000 Wired to Wireless, No Brand to Branded. I would suggest Xu Jia Hui Metro City or Hong Kong Plaza you will end up paying 50-100RMB more for them but at least some people will speak English.