EL ARISH, Egypt — Large caches of weapons from Libya are making their way across the Egyptian border and flooding black markets in Egypt’s already unstable Sinai Peninsula, according to current and former Egyptian military officials and arms traders in the Sinai. Egyptian security officials have intercepted surface-to-air missiles, most of them shoulder-launched, on the road to Sinai and in the smuggling tunnels connecting Egypt to the Gaza Strip since Moammar Gaddafi fell from power in Libya in August, a military official in Cairo said. Arms traders said the weapons available on Sinai’s clandestine market include rockets and antiaircraft guns....