In the 2006 reprint, which I studied from, there is a foreward to the 3rd edition. It’s not clear which of the printings (1996, 1998, 2000, 2003, 2006) align with the 3rd edition, but it is the only additional forward included in this printing. It says: “I would like to express my thanks to my friend Dr. Arndt Wigger for his assistance in enhancing the typography and design of this third edition of Learning Irish. While these improvements along with some minor updating of the material have resulted in changes in the pagination, the text of the previous edition remains essentially unaltered.”
I’m guessing there are no significant differences between the version of the text you have and this latest 2006 printing. I’ve looked briefly and have not found a source of the CDs alone. I bet there are thousands of unused tape players laying around in dusty corners, waiting for someone like you who will make use of them again.