I live in Atlanta, the only thing I can think of as "rare" is psychedelics. i.e. Mushrooms, LSD, and the like. This is only because my old phone was stolen and I haven't been able to get those connects back. Before my phone was stolen I could always solve a random boring day with some LSD or something profound. And it's not like they aren't around anymore, or even rare, they are just low-key. That's all I can think of though, everything else seems to jump out at you.
Maybe its the people I hang out with, or maybe its just a city like Atlanta is a pretty diverse place with interstate highways from coast to coast going through middle, and a lot of things transfer through here on the way to somewhere else. We have the mexican ghettos with their brickweed and imported shards, we have the black ghettos slangin' dat cocaine and heroin, we have the college-age jewish people selling their pounds of dankness, we have the trailer park folk with their bathtub methlabs blowin' up the neighborhood, got the rednecks 15 minutes away that aint 'ever been to the "city" only as far as ma's but can make you some damn fine moonshine and feed you freshly picked fieldie shrooms, even have a decent psychedelic scene with their raves and groovy vibes that i have been away from for way too long. every stigma you can think of calls Atlanta home, and "The City Too Busy to Hate" is more than willing to let you have the ability to let loose in whatever fashion you care for, and even in a couple ways you don't haha.
If I had to really go with something thought, I would guess maybe PCP? Only seen it a handful of times but never really cared to go out of my way for it, its just not this city's thing I guess. People in the ghetto don't even seem to like it. I've only used it once when I was offered to smoke a blunt by a random black guy that was in my house, sitting alone in my living room, when i walked in at 3am (weird story). I wasn't told that it had PCP on it, and I got fucking retarded. I was pissed when I found out, due to the shit that I was feeling and seeing. Never again, you couldn't pay me to smoke that shit now.