All issues of Gramophone magazine are now available online in full text (though one has to register for access to the PDF scans). One can search the archive and narrow the results down by decade and year. There are some 1500 results for electronic music and about 200 for concrete music. However, not all of these are reviews. The term electroacoustic music is only used in reviews from 1990 onwards, and 'acousmatic' not at all.
In the very first review of musique concrète, the reviewer, L.S., concludes: "To the intellectually curious, this disc will be of great interest: whether this is what we look forward to as the music of the future is another matter, not [to] be entered into here." The record reviewed is the Pierre Henry/Pierre Schaeffer Ducretet-Thomson DTL93090, containing Bidule en Ut, Schaeffer's 1955 Etudes, Henry's Le Voile d'Orphée and other works.
The overall tone of the review is a mix of condescension and prejudice: Neither Schaeffer nor Henry is counted amongst "real composers", unlike Boulez or Messiaen, despite the fact that Henry studied both with the latter and Nadia Boulanger, and the review begins with the usual science-fiction reference.
Well, at least something has changed for the better; I daresay reviews like this are more unusual today.
Thanks to InternetBrus for the tip.