I can share my experience of generating leads to some online casinos in Russia (that was not easy, as you can tell). Gambling is not allowed in Russia, so I had to use really smart techniques. How effective they was? You can check - just paste the url https://onlinecasinos.com.ua/bonus.htm and see site's position in google.
what I've used:
found leads in Twitter
optimized informative content at the website
automated marketing through Drip