Definition of "unobtainable"

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.

1979 August, Michael Harris, “A line for all reasons: the North Yorkshire Moors Railway”, in Railway World, page 412

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.

2018 January 1, Donald McRae, “The Guardian footballer of the year 2017: Juan Mata”, in the Guardian‎

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

1896, The American Journal of Philately, volume 9, page 294

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 […]

1975, Gerald Zaltman, Philip Burger, Marketing research: fundamentals and dynamics, page 293