Many Neo-Thomists believe that some version of the principle of sufficient reason is true. As far as I know, Leibniz was the first to coin the term “principle of sufficient reason.” But some Neo-Thomists hold that the principle can be formulated in a non-Leibnizian way — even in a Thomistic way — and legitimately employed.
Interestingly, it is not only a single homogenous group of thinkers in the Thomistic tradition who maintain this view but people who are often thought to be in many respects quite different from each other. Consider, for example, that both Reginald Garrigou-Lagrange and W. Norris Clarke subscribe to some version of the principle of sufficient reason.
I do not have time at the moment to go further into the topic. But if it is one that intrigues you, you should check out the recent discussion between Thomas Osborne and Steven Long at Thomistica.net. You can find Osborne’s first post here and Long’s reply here. Also look at the comment boxes for both posts to see further precisions and exchanges.
Clarke does not figure in Osborne and Long’s discussion but Garrigou-Lagrange does. Besides Garrigou, the principal dramatis personae of their discussion are: Leibniz, Afrikan Spir, and Étienne Gilson.