These things always go in cycles of feast or famine (so to speak).
When I was searching for a SN95 Saleen two years ago there were weeks when several were available & some weeks when there was nothing on the market. The time of year does have some impact on the availability of vehicles for sale, particularly specialty models like a Saleen. All those dealership myths about sales of convertibles peaking in the spring/summer do have some validity.
However, as the years progress the availability of quality Fox body Saleens are naturally going to diminish since they were very limited production to begin with. Subtract those that have been abused, neglected or otherwise wrecked & you have an even more limited pool of specimens.