Where have you been advertising? Places with NSFW content tend to have much lower ad prices because most advertisers won't touch them, but many of them (4chan and Danbooru come to mind) are probably pretty good for the audience you're looking for.
I agree! Twitch.TV might also have channels that you could send some candy to, and see if they would advertise Candy Japan to their viewers. While it's a bit different from the usual content, G2A (sells games) got a huge boost (the site even died a few times because of the traffic) from Lirik's referral link.
