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?
You can contact the casino itself and rent or sell your script to them but it's a lesser chance so you can contact the game aggregators like SoftSwiss who mediate things from acquiring games from developers and provide it to casino platforms. Just keep in mind game provider and game aggregators are two different things so pragmatic play is your competition who build their own games and sell it to the casinos so they are your competition. 