introuvable
adjective
in·trou·va·ble
aⁿ‧trüvȧbl(ᵊ),
-b(lə)
: impossible to find
pamphlets, all now almost introuvable 
Times Literary Supplement
Times Literary Supplement introuvably adverb
ə̇n‧ˈtrüvəblē
Word History
Etymology
French, from in- in- entry 1 + trouvable capable of being found, from Middle French, from trouver to find (probably from—assumed—Vulgar Latin tropare to compose) + -able