The Mirage website is (miraculously) still up and provides a list of the comics:
Volume 1 was reprinted in various collections and omnibuses, so it's not hard to find.
Issues of Volume 2 are pretty cheap online.
Volume 4 is harder to get your hands on.
Volume 3, which is considered not in the Mirage canon, was published under Image. It's often referred to as the "Image run." It was republished in color by IDW in recent years under the "Urban Legends" name.
For additional stories, you could also check out Tales of the TMNT:
If you want to read them in "chronological" order instead of order of release date (I don't recommend), then use this guide: https://tmntentity.blogspot.com/2010/01/mirage-comics-continuity-timeline.html
