As an overview you can refer to USGS mineral resources data base: https://www.google.com.tr/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&ved=0CDgQFjAB&url=http%3A%2F%2Fminerals.usgs.gov%2Fminerals%2Fpubs%2Fcommodity%2Fgallium%2Fmcs-2012-galli.pdf&ei=d_BcU6rONuiJyQPx6ICQAg&usg=AFQjCNGypjhyE-uzu_t-L8e3knF6zYnznw&bvm=bv.65397613,d.bGQ&cad=rja
Also Roskill publishes a report named "Minor & Light Metals" every year, the 2014 revision features Gallium, the title will be "Gallium: Global Industry Markets and Outlook" and it will be out within 2 months. Other resources that may come in handy: