Just a couple of brands:

http://en.thl.com.cn/

http://en.zopomobile.com/

http://europe.oppostyle.com/

http://www.ejiayu.com/en/

Here you can find other name for searching (no affiliation whatsoever with this shop, I don't even know if they sell in US, it's only the place where a couple of friends bought their chinese smartphone): http://www.grossoshop.net/Smartphone_Dual_Sim_Android_Proces...