LOS ANGELES — Most of the nearly 60,000 Central American children who have arrived on the U.S.-Mexico border in the last year still don’t have lawyers to represent them in immigration court, and advocates are scrambling to train volunteer attorneys to help cope with the massive caseload. With the number of unaccompanied immigrant children more than doubling this past fiscal year, the need for attorneys has surged, and it has been exacerbated by the immigration courts’ decision to fast-track children …