With performers like Ricky Martin and Jennifer Lopez burning up the airwaves, New York’s long, hot summer may require one more adjective this year: Latin. But popular acts notwithstanding, where can you find some música auténtica? Platinum-selling merengue superstar Sergio Vargas goes to La Movida (1610 St. Nicholas Avenue, at 190th Street; 781-8575). “They have music that’s hard for me to find,” says Vargas, plus “I’m also hanging out with old friends.” With only 3,500 titles in stock, La Movida won’t be mistaken for a Virgin Megastore, but that’s no problem for Vargas. “I get every album I need there,” he notes, including his favorites: salsa king Ruben Blades and merenguero extraordinaire Johnny Ventura.