I couldn't make contact with a librarian through the German or Italian sites either, though I tried. The latest address may help.
In the end daphnis' suggestion was sound: there is a copy in the Harvard music library. I easily made contact, with Evelyn Santana-Nola, and she sorted it out. Email: email@example.com.
They offer two options: access to a digitised version on their server, or a paper copy. For this score, the paper version was better. The score isn't of good quality, with yellow paper, and small noteheads, so I couldn't get an easily readable version from their own scan. But the paper version, for which they charged $25 via FedEx, which I thought was reasonable, was fine, and I was able to enhance the contrast and enlarge it to A4 (the Americans really hate the Europeans, even down to their paper sizes).
We ran through it last week, and it is a reasonable arrangement, though needless to say, as a pianist, I didn't think there was enough piano! It's a complex work, so we'll need to work on it. I was surprised that my excellent string playing colleagues weren't familiar with the work, and didn't seem too comfortable with the string writing -- though the core of the work is strings, even in the original. There's an optional part for second cello.
I'd be interested to hear what you think of it. If anyone knows of any other transcriptions like this, for piano trio/quartet/quintet, please let me know.