Word request for an academic paper/article that is 'hidden', 'difficult to find'

single-word-requests

obscure might work; it combines feelings of "concealment", "hard to get to" and "relatively unknown".

Here is an example of its use on one of our sister sites, MathOverflow:

How to locate an obscure paper?

A colleague asked me to locate the following paper on the web:

Kovalenko, I.N.: On the reconstruction of an additive type of distribution based upon a sequence of independent trials. Memoirs of the All-Union Conference on Probability Theory and Mathematical Statistics, Erevan 1958.

After a few failed attempts, I asked myself, how would I go about locating this paper in the REAL (not virual) world? What library stocks proceedings of the All-Union Conference... in Erevan, from 1958?

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