I have published on my page two fonts of the capital letters of the "Graduale Romanum" of 1908. They were given to me by a close friend of the late Holger Peter Sandhofe. I suppose there are no restrictions for its diffusion. If anyone knows of any, please notify me.

Fonts Solesmes and HPS Antiphonale: https://sites.google.com/site/gregorianicantus/1-fuentes-musicales?authuser=0#h.p_aY34sgcJETS2