A very good piece! Take a listen if you haven't heard it.
http://www.youtube.com/watch?v=_GnCeMxPchc
Worldcat lists this as probably the recording from 'Netherlands : Radio Nederland Transcription Service : BFO, Centre Netherlands Music' (whether ever commercially available, I don't know). Score's available from IMSLP and the piece has been recorded commercially twice I believe (unlike most of his other cello sonatas, though to be fair there are or used to be recordings of about 10 of them out there that can still be heard on internet-streamed archived radio if you search Google for (rontgen OR röntgen) site:concertzender.nl/programmagids.php - only pay attention to dates late 2006 and more recent, for only those can be listened to on your computer :)
Eric
It's a wonderful piece. The best recording's the one on MDG/Audiomax.