You can contact any agent you like, it does not have to be from the same agency. I recommend that buyers to a bit of research, read agent profiles, meet with a few different agents and find the one that you are most comfortable working with and then move forward with looking at properties. Keep in mind that a listing agents priority is to work in the best interest of the seller, therefore, your interests will come second. For example, a listing agent is going to negotiate towards getting the highest price and best terms for the seller, while the buyer's agent is going to negotiate to get the lowest price and terms for the buyer. Good luck in your search!