I played the original three Lemmings on PC many years ago. I'm sorry if this is addressed elsewhere on this site, but could someone direct me to where I can obtain copies of the Lemmings series, including a list of the main programs that are available"

Unfortunately, I do not believe that the original Lemmings games are available in stores anymore.  My suggestion would be to try Ebay and search for "Lemmings."  You can often find something there.

This issue was addressed about a month ago in the topic, "Buying Lemmings."  There are several more replies to your question there.