The best researching tool at your disposal is the publisher’s website. On that website, you can find historical information, plot synopses, list of past performances, even scores and recordings. Here are the websites I have used to make this database. If the work is in the public domain, check out imslp.org for scores.
BabelScores: https://www.babelscores.com/
BabelScores contain the following publishers:
Babel Scores
Edition Juliane Klein
Le Balcon Edition
Zerboni
Bärenreiter: https://www.baerenreiter.com/en/
Bärenreiter contains the following publishers:
Alkor
Bärenreiter Verlag Kassel
Carl Fischer
Editio Bärenreiter Praha
Henschel Verlag
Lemoine
Bill Holab Music: https://www.billholabmusic.com/
Boosey and Hawkes: https://www.boosey.com/
Canadian Music Centre: https://cmccanada.org/
Carl Fischer: https://www.carlfischer.com/
Chazz Mack Music: Chazz Mack Music is the publisher of Charles McPherson. You can find his music here: https://charlesmcpherson.com/
Contemporary Music Centre Ireland: https://www.cmc.ie/
Dilia: http://www.dilia.cz/
Donemus: https://webshop.donemus.com/action/front/home
Dreiklang-Dreimasken: https://www.dreiklang-dreimasken.de/
ECS: https://www.ecspublishing.com/
Edition Peters: https://www.edition-peters.com/
Edition Peters contains the following publishers:
CF Peters Musikverlag
Edition Kunzelmann
Edition Peters
Edition Samfundet
Edward B. Marks Music Company: https://www.ebmarks.com/
Faber Music: https://www.fabermusic.com/
Fennica Gehrman: https://www.fennicagehrman.fi/
Gehrmans: https://www.gehrmans.se/
Josef Weinberger: https://www.josef-weinberger.com/
Keiser Southern Music: https://www.keisersouthernmusic.com/
Musica Brasilis: https://musicabrasilis.com
Oxford University Press: https://global.oup.com
Peer Music: http://www.peermusicclassical.com/
PromoMusica: http://www.promusint.com/wp/
PWM: https://pwm.com.pl/en/stronaglowna/
RAI Trade: http://www.edizionimusicali.rai.it/en/
Ricordi: https://www.ricordi.com/en-US/ or Durand, Salabert, Eschig: https://www.durand-salabert-eschig.com/en-GB/
Ricordi and Durand, Salabert, Eschig contains the following publishers:
Durand
Eschig
Forberg
Ricordi
Salabert
Schott Music: https://en.schott-music.com/
Schott Music contains the following publishers:
Ars-Viva-Verlag
Astoria Verlag
European American Music Corporation
Gershwin Music
Schott Music
Sidmar Music
Zerboni
Skayne’s Music: Skayne’s Music is Wynton Marsalis’s publisher. You can find his music here: https://wyntonmarsalis.org/
Sonzogno: https://www.sonzogno.it/
Subito Music: https://www.subitomusic.com/
Theodore Presser: https://www.presser.com/
Transformation Art Publishers: Transformation Art is the the publisher of works by Fred Ho. His archives are in the libraries of Harvard and the University of Connecticut.
Tri-Centric Foundation: https://tricentricfoundation.org/ Tri-Centric Foundation publishes and records the music of Anthony Braxton.
Universal Edition: https://www.universaledition.com/
William Grant Still Music: http://www.williamgrantstillmusic.com/
Wise Classical Music: https://www.wisemusicclassical.com/
Wise Classical Music contains the following publishers:
Alhambra RXR
Alphonse Leduc
AMP Inc
Associated Music Publishers
Breitkopf und Härtel
Chester Music
Choudens
Dmitri Shostakovich Estate
Domenico Music Notes
Dunvagen Music Publishers Inc
Edition Wilhelm Hansen
Editions Transatlantiques
EMI Music Publishers
G Schirmer Inc
Gehrmans
Hans Sikorski
Hans Sikorski Russian Works
Heugel
Margun Music
Novello
Schirmer Russian Music
St. Rose Music
Tempo Music
Zarathustra Music: Zarathustra Music is the publisher of Eliot Goldenthal. You can find his music here: https://www.elliotgoldenthal.com/
the Operatic Saxophone 