Thanks to the Bibliothéque nationale de France, most of the 67 volumes of the Acta Sanctorum are available online. Since accessing each volume and then finding what it contains is quite time-consuming, I've just bookmarked each of them, giving the days of the month each contains (it lists all saints whose commemorations occur on those days), and put them in my list of sites I refer to.*
Unfortunately even the National Library of France doesn't hold all volumes; maybe they're online elsewhere... (By Murphy's Law, any saint I'll want to find out about will have his feast day on one of the dates contained in an unavailable tome.) So these volumes listed below are NOT available, and hence 22% of the year remains uncovered:
A.S. Martii (T. 2 / 9-18 Martii)
A.S. Aprilis (T. 2 / 11-21 Aprilis)
A.S. Novembris (all volumes except T. 4 / 9-10 Novembris)
A.S. Decembris (Propylæum; the series remains incomplete)
*Oops, dangling participle! "This is the sort of thing up with which I will not put" – Churchill.