It’s hard to precisely predict what annuals and perennials will be available on exactly which days in the future, but the Plant Club website is a good starting point. Clicking on this link https://northshoreplantclub.com/list?all=1&t=10 shows perennials which were available at some point last year. Some plants that you see will be shaded out because those plants cannot be purchased now.
Some plants are only grown or available at certain times of the year. The individual plant detail pages have a “Pricing and Availability History” area which shows the dates that plant was available in the past in what sizes. Often those dates and sizes are good predictors of what might be available this year and when nurseries might have a crop of them, but new plants replace old ones, plant propagator, grower and purchaser plans change. Sometimes plants intended to be sold don’t work out!
We'd recommend saving the item you're looking for to your Wishlist from the plant detail page. When you're logged in, you WishList will tell you if any of those plants are currently available!