: This digital library offers free public domain versions of the "Solfège des Solfèges" series. While Volume 1 is most common, you can search their Solfège Collection for later volumes.
: The go-to source for public domain scores. Search for "Solfège des Solfèges" to find various volumes and editions. Internet Archive solfeo de los solfeos 4 pdf
Because the original Dannhauser work was published in the late 19th/early 20th century, the copyright status varies by country. In the US, works published before 1928 are generally public domain. However, many modern editions (like the Lemoine or Ricordi editions) are still under copyright. : This digital library offers free public domain