There is no legal way to purchase a monkey in the United States, as most species are endangered, and it is illegal to own one as a pet. Unless you are a zookeeper, scientist, or other qualifying professional who requires a monkey for a specific purpose, it is not possible to purchase one.
Instead, potential buyers must contact a wildlife rehabilitation facility or primate sanctuary to inquire about adoption or fostering a monkey. In some parts of the world, such as Thailand or Indonesia, it is possible to purchase a monkey, although monkey owners must have a permit, and it is still considered unethical due to the legal and emotional/physical needs of the primates. Additionally, it is important to remember that monkeys are wild animals, and require specialized care and resources that may not be available in your home.