dependent drop down list

Hi,

I am trying to apply a formula for dependent drop down list which I got from net to my worksheets. Look like it is working fine when I select the region name and then show province name of that region in another drop down list (My columns are in this order: Location, Region, Province)

However, I now would like to do the reverse by select the province then the next drop down list would show value of the locations in that province (My columns are in this order: Location, Region, Province)

I have attached my sample along. Your advice will be very much appreciated.