So you figured out that monogamy isn't for you and you're ready to get your polyamory on? There's a world of delicious people just waiting to be fallen in love with. Just one problem: Most of them aren't poly—at least, not yet.
Thus, the eternal dilemma. The already-poly dating pool is small. I strongly prefer dating people who haven't already been partners with half the women I know. But I'm also averse to trying to convert anyone. When I remember the headaches and heartbreaks of dating people who weren't cut out for polyamory... it's enough to make one stay in the incestuous little petri dish forever.
Still, one notices attractive strangers, and sometimes they're noticing you back. I'm not advocating for snap judgments, and there's no perfect system for determining if someone will still view you as a romantic possibility once you've said you're poly. But I do have a formula for making that split-second decision between "Talk to him, you never know" and "Not a chance in hell." The list is far from comprehensive, and I've certainly disregarded the rules myself. But here it is: Mistress Matisse's Poly-Possibility Field Guide.
Easy one first: Hipsters? Forget it. Being polyamorous requires displaying emotions other than jaded contempt. It cannot be done ironically, and hipsters can't claim to have liked polyamory before it was cool, because it hasn't been cool yet. Epic fail...
Nerds? Chat them up. Nerds are defined by their inability/unwillingness to conform to popular manners and style, so they're usually open to discussion about nonconforming romances. (I've previously discussed their strong stamp upon the BDSM community.) I can't speak for nerd girls, but I've found that when I tell a nerd guy that, theoretically, he could have two girlfriends—one of them being me—he generally doesn't find that idea unattractive.
Hippies? They already are poly. Okay, that's not literally true. But the demographics of the visible polyamorous social scene skew heavily toward hippies. They have old-school cred, for one thing. No one uses the term "free love" anymore, but it is part of hippie history. So anyone identifying with hippie culture is unlikely to instantly reject you for being poly.
Punks? Highly doubtful. Punk is a term that defies easy definition. But let's say that punks are people who have a working-class identity and actively reject and rebel against middle-class—particularly hippie—values. Punks prize authenticity and scorn poseurs. Thus, if a punk sees polyamory as a betrayal of his/her core principles, your flirtation will go badly.
I've been rather flippant here. But seriously, no matter what subcultures they participate in, people are individuals. You can't really make an accurate judgment about someone based only on labels—you just have to put yourself out there. And whether you're polyamorous or monogamous, the best partner to have is someone who values loving acceptance of one another's individuality, and mutual cooperation over competition. That's someone with potential.