Huh? How did I not know about this?!? There’s an publishing house called the Alexander Street Press that has a website devoted to literature from the Catholic Reformation, on which you can find the works of classic Thomistic commentators such as Thomas de vio Cajetan, Domingo Báñez, Menchior Cano, Domingo de Soto and Francisco de Vitoria. The main page for Digital Library of the Catholic Reformation is publicly accessible, but further access seems to require some subscription (my access is possible through Marquette University’s subscription).
The site contains the Opuscula omnia of Cajetan, including his De nominum analogia, De conceptu entis and his commentary on Thomas’s De ente et essentia. Alas, it does not contain Cajetan’s commentary on the Summa theologiae. On the other hand, Báñez’s Scholastica commentaria for the Prima pars as well as the Secunda secundae is to be found there, as is Cano’s De locis theologicis, and Soto’s De natura et gratia. De Vitoria’s holdings are simply his Relectiones theologicae, but these contain interesting material on ecclesial politics and power, as well as discussions of war-making in the New World.
In keeping with the Reformation-focus, the Alexander Street Press also has a Digital Library of Classic Protestant Texts, as well as a similar resource on Karl Barth.