Surface-to-air missiles pilfered from army bases. Defectors from Ukraine’s elite special forces. Russian fighters who slipped across a porous border. These are some of the biggest problems facing Ukraine’s military in the rebellious east, and they were all on prominent display here in the unlikely setting of the Donetsk Botanical Garden , where the Vostok Battalion, the largest separatist militia in this city of one million people, has established a training camp. “We are an international battalion,” said Aleksandr Khodakovsky, the rebel commander, who led the government’s Alfa special forces unit in the Donetsk region until he resigned after the February revolution in Kiev. Mr. Khodakovsky said that Russian citizens were among his fighters, but that the “overwhelming majority” of his force of more than 500 came from eastern Ukraine. He denied any link to Russia. As the threat of a Russian invasion into eastern Ukraine […]