The developing states were the main sources for all skilled and unskilled labours. However due to the real state development in all tire 2 and tire 3 city, the availability of labours are reduced in all major cities. To know more about the scenario you can refer the story Construction pace impact by dwindle labour migration, at commonfloor.com
All the Metros are getting the skilled and unskilled labours from different underdeveloped states of India like Bihar, Rajasthan, UP etc. The unskilled youth migrates to the cities in search of job opportunity.