1. Ask yourself why you want to do agency work, especially somewhere where you're breaking the law too and agencies are a bigger target than independents.
2. Pretend you're a client, find out about some and then see if they're looking for more escorts.
Can you work legally in the US? Whether what you're doing is otherwise legal or not, being caught working in the US when you're not allowed to do so is one way to cross it off your list of places to visit for a very long time.