Schuler "upon demand" did offer tubes, at least on the O/Us, by Wittener Excelstorstahl, Krupp Spezialstahl and Bohler Antinit. As to yet, I can't find that they offered Rochling/Roechling(Rochling Eisen and Stahlwerk with Carl Rochling(1827-1910-not the artist) and Hermann Rochling(1872-1855) - -
http://www.saarstahl.com/geschichte_voelklingen.html?&L=1 , who appear to have been tightly connected to the Nazis and the French De Wendel folk.
Merkel in the mid 1920s offered tubes of Krupp, Roechling, Poldi and Boehler steel.
Other steel makers with a presence in Germany:
Fasterstoff - little info yet,
Skoda -
http://www.quel.nl/Toeleveranciers/skoda-steel/19041 Witkowitz / Vitkovice Iron and Steel Works in Moravia was owned by the Austrian Rothschilds with partners brothers Wilhelm and David von Gutmann. It appears to be/have been Jewish.
I also forgot Thyssen - Friedrick Thyssen -
http://en.wikipedia.org/wiki/Fritz_Thyssen .
Kind Regards,
Raimey
rse