Those stores buy from wholesale nurseries that produce HUGE volume. These producers, to qualify to do business with a regional chain of Home Depot, WalMart, Lowe's, Target, etc, they must be able to supply ALL their needs, stock ALL their stores. You can understand that the wholesalers need "safe" items to propagate: sometimes they will cover a whole acre of land with one type of plant.
These large wholesale nurseries can't be bothered with specialty items. People want petunias,
pansies, broccoli, tomatoes, herbs, etc. in September in the South. Imagine the huge surge of plant stock going to Phoenix in the Fall season: Lowe's - 8 stores, Target -18, Home Depot - 20 and countless WalMarts, all loading up with the most popular plants.
You can perhaps find your carnivorous plants, succulents and cacti at a locally-owned nursery.
Another possibility is to order from a catalog. Look up the plant you want by Google search.
Find a list of nurseries that offer the item you want. If one of them is local, you can drive over
to pick it up. Don't give up, someone can get it for you.