Can cambodian passport holder make a new L visa in Singapore?

Hi, I am Cambodian passport holder already in China for 2 months. Originally came here on a one month L visa arranged in Cambodia then extended it one for one month in China. Is it possible to fly to Singapore and to make a new L and then come back to China? If so, what documents are needed? what is the cost and the fastest process time? What is the maximum lenght of the L I can get?