大海捞针

Explanation: A needle in a haystack. Analogy is extremely difficult to find. 　　Usage: Partial official; as object, attribute, adverbial; for Figures of Speech in 　　Source: Ming Wang Ling "Spring Wuhu in mind a scheme": "seek benefits such as needle in a haystack, like dry wood fire stir trouble." 　　Examples: To inquire about the whereabouts of the former inspection magistrate families, then it is ~ in general, asking for a long time, no one knows. (Qing Wu Jian "Twenty years Strange" Article seven times) 　　Riddle: Monkey King by underwater treasure Thesaurus:  not likely to happen in a century, once in a blue moon, walk with difficulty, Impossible and, Sea Fishing, Makes all things easy, bark [bay] at the moon [bay the moon], the sound of footsteps in a deserted valley-a news or a statement which one does not hear often,or a thing that was seldom to found, Rarities, once in thousand years, sth.seldom seen or hardly possible as the iron tree blooms, Hard-won, defy Beyond the bounds of, strength of nine bulls and two tigers,mighty force, doomed petition like asking a tiger for its hide, Leather and Fox plan Antonym Group:  Have no choice but Shengji, Just to stoop and gather Are all, as thick as June blackerries, ubiquitous, overrun, cataclysm crosscurrent, Attracting attention Are all, common and numerous, Even flat-bed truck