Volumes 1 and 2 were published in 2007; volume 3 is a supplement just published in April 2012.
A co-author and I wrote the entry on "Tolkien." The Kindle edition is reasonable in price for personal purchase (see this link). If you go to the Amazon website and use the "Look Inside the Book" feature, you can search for "Tolkien" and read the article.
For hardcover purchases, interested readers should likely contact their local public and college libraries and suggest purchase of these volumes for the reference section. You can make the request in person at a library or email a request to the local librarian or the staff librarian in charge of collection development or of the reference collection.
Here is a suggested message to your local public or college librarian:
(If your local library already has the first two volumes, then suggest the purchase of Volume 3. You should include in your message the ISBN, which is a number that conveniently and accurately identifies a book.)
"I would like to suggest an addition to the library's reference collection: the Catholic Encyclopedia of Social Thought (Volumes 1 and 2 published in 2007; Supplemental Volume 3 just published in 2012), by Scarecrow Press, a division of Rowman & Littlefield. E-book versions are available.
The ISBN for the volumes are:
Vols. 1 & 2: ISBN/9780810882447
Vol. 3: ISBN/9780810882669
Here are some relevant links:
Amazon.com: Encyclopedia of Catholic Social Thought, Social Science, and Social Policy: Supplement: 3 ; Encyclopedia of Catholic Social Thought, Social Science, and Social Policy (2-Volume Set)
Publisher's website: Volumes 1 and 2 (https://rowman.com/ISBN/9780810882447#); Volume 3 (https://rowman.com/ISBN/9780810882669#)