unobtainable

adj

1. Unable to be obtained: not able to be acquired or reached.

   “With secondhand bullhead rail almost unobtainable, the NYMR has been forced to go for new flat-bottom rail and orders are being placed; 58 fb rails are already en route to the railway.”

   “Common Goal’s grand ambition is to reach a position where 1% of football’s entire multibillion dollar industry is donated to charity. It might seem an impossible dream – just as a young boy’s fantasy of becoming a top footballer almost always seems unobtainable. But Mata was one of those who fulfilled his footballing dream.”

noun

1. Someone or something that cannot be obtained.

   “On the whole they are at present fairly cheap, and are not overburdened with long priced stamps, and still fewer unobtainables.”

   “Refusals, or unobtainables, are difficult to predict, but seem to be affected by the nature of the respondent, the sponsorship of the study, and the nature of the questions. Some refusals are definite and final […]”