I feel like I've got a fair bit of experience with this. Over the years I've gotten several women to cuckold me. Believe it or not Tinder or main stream online sights have worked well. It's not a matter of finding someone who is automatically into it but rather someone who is open sexually.
I throw out feelers with the women I chat to to get an idea of how naughty they are, are they don or sub, are the into black or not. You can find all this out just by chatting and not giving it all away.
Eventually you have to take the plunge once you've found a woman who is freaky and finds black men attractive. Bring it slowly, talk about watching, talk about cuckolding. Most women who like it don't even know what it is. You'll find most are not into it but you'll also find that there are more than you'd think that like it.