I represent brokers based out of Texas. What you want is a noncircumvent provision in your brokerage contract. There are many ways to do this. One way is to be Company A's sales agent to the customer and that orders for the product by that customer will result in a commission to you, and to make the agreement for at least a certain amount of time. Of course, if you are buying and reselling, you aren't exactly just a broker, and the relationship you're describing could have additionally complications. You should sit down with an attorney in California who can take the time to ask questions and understand your business more in-depth.