Dear Andrea,
In response to your query, the Fantasy recording of Le Testament is out of print.
You could search for it with used record stores or brokers of out of print LPs.
Fantasy Records #12001, 1972.
There was a Dutch recording - also out of print - Holland: Philips: #9500 927, 1980
which could be tracked the same way.
Put out a call on the internet for these recordings.
The archives (Beinecke at least) may have audio tape recordings you could listen to.
Or university libraries may have the recordings.  The Stanford Archive of Recorded
Sound probably has copies (Stanford Univ., Palo Alto, CA)
The B.B.C. Sound Archive Library (London) has the audiotape of the 1962 broadcast
produced by Murray Schafer and D.G. Bridson.
Best wishes,
Margaret Fisher