Does anyone know where to find Britannica's Great Books of the Western World in the Red Cover Vol. 17&19?

A friend of mine has almost the entire 60 vol. set, but he is missing Vol. 17 (Thomas Aquinas II) and Vol. 19 (Dante & Chaucer). It is the 1990 edition, but it has a red cover. All of the others that I have seen are in black, though. If anyone can tell me where to find the Red Cover 1990 edition or where to get these two volumes in the Red Cover, it would be greatly appreciated.