You can't get a L VISA in Seoul, the China embassy in Seoul asks applicants other than Korean to provide Alien Registration Card valid for at least 6 months.

I'm US citizen, teach English in Seoul, My ARC has only 3 months remaining validity in August, I want to get a L visa to China to visit Beijing, Shanghai, however, the travel agency that authorized by the embassy said that I can't apply for a L visa because my ARC is valid for only 3 months, I was advised to mail my paspsort and other documents to US and ask my family members to apply for visa for me, then I mail them to US and ask my mom to apply for L visa for me from China consulate in LOS Angeles, then I get the visa and my mom mail my passport back to me in Seoul.