Jewish Art Music (in the Sylvia And Harry Rebell Digital Collection of the Library of the Jewish Theological Seminary), check also: Yiddish
Thesaurus of OrientalHebrew melodies (collected and edited with an introduction by A. Z. Idelsohn, Berlin & Jerusalem, 1923-1932, accessible from the Jewish National & University Library)
Scores of Yiddish theater music, songs and arias arranged by Henry A. Russotto (Goldfaden, Mogulesco, Lateiner et al.), 1897-1915
Yiddish Songs (published music sheets) in the US Library of Congress
Music to Yiddish popular & oper(ett)a songs (in Judaica collection, Gothe Universitätsbibliothek F. a M.);
Yiddish Sheet Music (in the Brown University Library Digital Initiatives)
"Sheet music" (in the YIVO Institute for Jewish Research Digital Collections)
Sheet Music Consortium (search for "Yiddish" yields old american pop songs with some Yiddish/Jewish "humorous" motif)
Lyrics and scores of songs by Abraham Goldfaden (Free Download), Musikverlag Ulrich Greve: Nürnberg, updated: January 2018 (asdo here)
Lyrics and scores of Yiddish songs [Song lyrics in Yiddish and scores in MuseScore format (exportable to MusicXML) from Mordechai Gebirtig, Eliakum Zunser, Mark Warshawsky and others], Musikverlag Ulrich Greve: Nürnberg, updated: January 2018
עמאנועל (!) האקען, ניגונים צו יידישער דיכטונג, באנד 1, אור-תו: תל אביב, 1973
עמנואל האקען, ניגונים צו יידישער דיכטונג, באנד 2, אור-תו: תל אביב, 1974