Important Note: Reaching out to agencies can be difficult; they receive many applications, and a lot of times, you are not hearing back from them. Try to contact as many as possible, and if you don't hear back from them, try it in 3-months again. Be persistent, and just don't give up!
Another way to getting signed with major agencies around the world is to sign with a "mother agency." A mother agency functions as your manager, with direct contacts to major agencies around the world, it's easier to get your foot in the door. A mother agency will scout, develop you as a model, and will direct your modeling career, handling contracts, and negotiate your rates. You will have peace of mind and can solely focus on your modeling jobs, instead of worrying about the business side of the industry.