This is probably more than you want, but since I have PDFs of the reference books...
- Claude Bolling (classical/jazz hybrid) Sonata #2 - for 2 pianos with percussion and double bass
There's this list from Hinson's "Music for More Than One Piano - an annotated guide":
Appendix II: Music for Piano, Four Hands with Voice(s) and/or Other Instrument(s)
(See main listing for full reference)
Abeille, J. C.: Grand concerto (orchestra)
Arnold, Malcolm: Concerto (orchestra)
Berens, H.: Gesellschafts-Quartets (string quartet)
Binkerd, Gordon: And Viva Sweet Love (voices)
Böhm, J. C.: Wechselgesang (voice)
Bois, Rob du: Deuxième Série de Rondeaux (percussion)
Boyd, Anne: Rain on Castle Island (voices, percussion)
Brahms, Johannes: Liebeslieder waltzes (voices)
Brant, Henry: Ceremony (voices, orchestra)
Britten, Benjamin: Noye’s Fludde, Op. 59 (voices, orchestra)
Czerny, Carl: Concerto (orchestra)
Dvořák, A.: Three Men’s Choruses, Op. 43 (voices)
Fétis, F. J.: Sextet (string quartet)
Fröhlich, F. J.: Concerto (orchestra)
Gaertner, Marie-Thérèse: Concertino (percussion)
Genzmer, Harald: Spielmusiken (instruments)
Ghiel, T. F. de: Sonata concertante (instruments)
Gutchë, Gene: Gemini, concerto, Op. 41 (orchestra)
Hastetter, E.: Eine kleine Krippenmusik (instruments)
Hauer, Josef Matthias: Zwölftonspiel (accordion)
Hauer, Josef Matthias: Zwölftonspiel (two violins, viola, cello)
Hauer, Josef Matthias: Zwölftonspiel (violin, cello, accordion)
Hoddinott, Alun: The Silver Swimmer (voices)
Hofmann, Heinrich: Minnespiel, Op. 42 (voices)
Hollfelder, W.: Kleine Tiergarten (voices, percussion)
Huber, Hans: Walzer, Op. 27 (instruments)
Hummel, Johann Nepomuk: Nocturno, Op. 99 (four horns)
Imbrie, Andrew: Concerto (orchestra)
Jadassohn, S.: Sextet, Op. 100 (string quartet)
Klebe, Giselher: Szene (four solo violins, tutti violins)
Klink, Waldemar: Kleines Lob der grossen Stadt (voices, percussion)
Köhler, Gottlob H.: Introduction et polonaise (flute)
Koželuh, Leopold: Concerto (orchestra)
Küffner, Johann J. P.: Sonate (two violins, two horns, cello)
Latimer, Ruel: Passacaglia and Fugue (clarinet)
Lee, Peter: A Conversation Piece (voices)
Marez Oyens, Tera de: Ballade grotesque (voices)
Mažek, Vincenz: Concertino (orchestra)
Masséus, Jan: Gezelle liederen (voice, percussion)
Mater, E.: Improvisaciones No. 1 (string quartet)
Mayuzumi, Tochiro: Sphenogrammes (flute, alto sax, marimba, violin, cello, voice)
McBride, Robert: Vocalise (voices)
Meale, Richard: Sinfonia (strings)
Mul, Jan: Concerto (orchestra)
Niehaus, Manfred: Einige Anweisungen für die Millelage (electric guitar, viola)
Nietzsche, Friedrich: Hymnus an die Freundschaft (chorus)
Noskowski, Siegmund: Fahrender Spielmann, Op. 18 (chorus)
Novák, Vitěslav: Dvě balady, Op. 19 (chorus)
Osieck, Hans: Suite concertante (orchestra)
Owen, Harold: Metropolitan, bas cantata (chorus)
Pijper, Willem: Op den Weefstoel (chorus, wind instruments)
Randhartiger, B.: Variations, Op. 11 (two horns)
Regner, Hermann: Klangspiele (percussion)
Respighi, Ottorino: Suite della tabacchiera (wind instruments)
Reynolds, Verne: Graphics (trombone)
Reynolds, Verne: Xenoliths (flute)
Rogalski, Theodor: Two dances (winds, percussion)
Santos, Manuel L.: Quintet (two violins, flute)
Schumann, Robert: Spanish love songs, Op. 138 (voices)
Senft, Luigi: Concerto (two violins, violin, bass)
Smith, Gregg: Songs of Innocence (chorus)
Smolanoff, Michael: Concerto (strings, percussion)
Studer, Hans: Kienes Konzert (instruments)
Tag, Christian T.: 12 Veränderungen (flute)
Tate, Phyllis: Hampstead Heath (woodwinds, brass, percussion)
Vogler, Georg Joseph: Concerto (orchestra)
Walker, George: Five Fancies (clarinet)
Wesley-Smith, Martin: To Noddy Man (voice)
Williams, David R.: Concerto (orchestra)
Williamson, Malcolm: The Happy Prince (strings, percussion, chorus)