Seen Carnivores at HD, Franks Nursery & Crafts(when it was around) Target in NY and independant nurseries, flower shops and Whole Foods in SF when I lived there.
Temperates in NY are usually sold in the fall, before they go into dormancy & sometimes billed as Halloween plants, a great thing to do is offer them little money for all their "dead" plants around mid-Nov to Dec.
Nepenthes in NY I've only seen at Frank's when they were around, I don't think I've ever set foot into a Lowe's..
SF the big times are spring & fall, but there's alotta places that got em year-round.
Plants I've seen in NY: N. ventrata & rafflesiana, low-growing flytraps & Dentae and finally for Sarra's I've seen Dixie Lace and Purple Venosa. Seen Big N. xMiranda's in the Flower District in NYC.
Plants I've seen in SF: Jeez, too many to list, some Orchid stores have big, varied collections of healthy plants for cheap. Little independant nurseries, Bonsai shops in Little Japan and even grocery stores have some varied collections as well.
Course just outta SF is California Carnivores greenhouse which is like Mecca for CP enthusiasts.. ya gotta go there at least once in your life.
You do get bigger plants for cheaper from shopping at non-CP stores, CP nurseries are usually best for hard-to-find plants really...
Hope this is informative and not too much of a chore to read