1908 unfortunately is earlier than both the coverage of l'Annee and Colby's holdings of Rheinisches Museum. I did find it in the bibliography of another article:
"Hugo Rabe's articles are entitled, 'Aus Rhetoren Handschriften' and 'Rhetoren Corpora' and appeared in Rheinisches Museum fur Philologie 62 (1907) 247-64; 63 (1908) 127-51; 512-30; 64 (1909); 284-309; 539-90; 67 (1912) 321-57."
I copied this information from Note 1 on p.196 of George Kennedy's article, "Later Greek Philosophy and Rhetoric" in v.13, #3 (1980) of Philosophy & Rhetoric, which is in JSTOR. I found another citation in another bibliography that gives the first title to the 1908 article.