Let's say for example, I created a game and I want it to be played in a gambling site? like who should I contact?
If you are a good game developer, after creating your game, you can contact a casino for them to review it and if it's superb, the casino will contact you after they must have checked it out if customers liked it. I believe that you want to use your skill for business, the casinos are the only sure ones to help you promote your game.
If he is good at developing games, its more better that he allows the gambling platforms review for his works and place demand, meanwhile, he can also choose to create a gambling platform and then include some of his games there, this is about how you're able to engaged people on what you offer, gambling is not what we can just do without people making a review about it, despite being a lucrative business, we have to be logical as well in it.
Additionally, OP may even contact some of the game providers to offer them services by introducing new games and the likes, if they like his works, then he can make business with some of them.