Zimerman has a following (I am one of his admirers) and, having been
fortunate enough to hear him play Brahms in Bristol a couple of years
ago, I can see why people might be particularly keen to get these
recordings.  Particularly if they are trying to assemble a complete
discography (he hasn't made that many recordings).

I have sometimes obtained recently deleted recordings through "German
Music Express", an Amazon partner company.  (Dislaimer: I have no financial
connexion with this company).  Failing that, you could cultivate
acqaintances in Japan, where otherwise deleted recordings sometimes
continue to be available.

Virginia Knight
Personal homepage: http://www.ilrt.bris.ac.uk/~ggvhk/virginia.html
Blog (mostly about singing): http://devbox.ilrt.bris.ac.uk/~cmvhk/blog/