It isn't the easiest show to watch because of the length of each episode. And if it is a clunker of an ep. (and there were many) that is a lot of time wasted, I don't feel as confident firing up the next episode.
I have seasons 1-3, 6, and 8(I bought them whenever I saw them at Sam's Club years ago).
Season 4 is still easy to find, 5 a bit harder, but season seven is crazy. I don't know if it had a low production run, but I don't see copies anywhere. I haven't checked for "The Men From Shiloh" yet...