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RISM A/I: Einzeldrucke vor 1800. Printed Music before 1800 (first editions). 9 volumes and 5 volumes of supplements. Arranged alphabetically by composer. Ref Is. M113 .I6 Ser. A v.1. pts. 1-15.
RISM B/I: Recueils Imprimés XVIe - XVIIe Siecles. First editions of collections between 16th and 17th centuries. Arranged chronologically by year. Ref Is. M113 .I6 Ser. B v.1.
Years 1500-1550 are available online at the above link.
RISM B/II: Recueils Imprimés XVIIIe Siecle. First editions of collections in the 18th century. Arranged alphabetically by collection title. Ref Is. M113 .I6 Ser. B v.1.
There is no single source for finding ALL early printed music.