It is not legal in many parts of the world to purchase a real baby monkey. It is also an illegal activity in the United States and in most other countries. Possessing a wild animal like a monkey for personal use is not supported by most animal protection organizations.
The best place to find and purchase a baby monkey would be through an organization that specializes in monkey rescue and adoption. If you are considering getting a baby monkey, it is important to ensure that the conditions are safe and the animal is being treated in a humane manner.