Johanna Gadski can be heard on a number of Mapleson Cylinders

http://www.mediafire.com/?ymmaoxgkzz0

As the LP notes, this is not high-fidelity sound. This is IRCC LP7006, issued in 1955, containing transfers of a number of Mapleson Cylinders, recorded live from the stage of the Metropolitan Opera House from 1901 to 1903.

Gadski appears on the following tracks:

4. Meyerbeer – Les Huguenots – Duet Act 3 (four fragments)
Johanna Gadski, soprano; Edouard de Reszke, bass. Philippe Flon, conductor
24/1/1903

6. Wagner – Lohengrin – Mein Held, in dem muss vergeh’n (Act 2)
Johanna Gadski; soprano; Georg Anthes, tenor. Alfred Hertz, conductor
7/2/1903

7. Wagner – Die Walküre – Herrlichste Maid! (Act 3)
Lillian Nordica, soprano; Johanna Gadski, soprano; David Bispham, baritone; Marguerite Marilly, soprano; Camille Seygard, soprano; Marie van Cauteren, soprano; Mathilde Bauermeister, contralto; Carrie Bridewell, contralto; Louise Homer, contralto; Marie Maurer, contralto; Ernestine Schumann-Heink, contralto. Alfred Hertz, conductor
21/2/1903