Books by Jacques Maritain:
Oeuvres complètes de Jacques et Raissa Maritain in 15 volumes. Editions Universitares Fribourg, Suisse, éditions Saint-Paul, Paris. The volumes are presented in chronological order. Notre Dame Press is publishing various volumes in English. Older English editions include:
_____ (1930) An Introduction to Philosophy. Translated by E.I. Watkin, Sheed
& Ward, NY.
Maritain, Raissa. (1961) Adventures in Grace, and We Have Been Friends Together. Garden City, NY: Image Books.
Kernan, Julie. (1975) Our Friend, Jacques Maritain. Garden City, NY: Doubleday & Co. (A good basic biography on the Maritains.)
Aquinas, St. Thomas. (1949) On Being and Essence. Toronto, Canada: The
Pontifical Institute of Mediaeval Studies.
Bañez, Dominic. (1966) The Primacy of Existence in Thomas Aquinas. Chicago: Henry Regnery Company. (Bañez was one of those Thomist metaphysicians who understood the primacy of the act of existence.)
Carlo, William E. (1966). The Ultimate Reducibility of Essence to Existence in Existential Metaphysics. Martinus Nijhoff: The Hague.
de Finance, Joseph. (1945) Etre et Agir. Paris: Beauchesne et ses fils, éditeurs. (One of the book that inaugurated a renaissance of existential Thomism.)
Gilson, Etienne. (1937) The Unity of Philosophical Experience. Charles
Scribners Sons: NY.
Johann, Robert. (1966) The Meaning of Love: An Essay Towards the Metaphysics of Intersubjectivity. Paulist Press.
John, Helen James. The Thomist Spectrum. NY: Fordham University Press, 1958. (On the different schools of Thomism.)
Many of these books are, unfortunately, out of print. Try your library's interlibrary loan system to see if they can borrow them for you.