recently saw a lot of material at the Museo del '900 in Milan.
The display shows project, pictures and the original tools used by Russolo build it.
This summer I saw a massive modern version of the Intonarumore at Fondazione Prada's Art or Sound exhibition,
http://www.prada.com/it/fondazione/cacorner#home!, which would be worth a visit even from abroad.
Unfortunately Russolo's device was not in action when I arrived.