Get involved in your local tennis community. Join local tennis clubs, ladders and leagues. After you play in a few scheduled matches that you have volunteered for (such as a men's doubles team), you'll get to know people that way. You build up a camaraderie with them and before you know it, you have ten people in your contact book that you can hit with at any time. It takes less time than you think, but you have to get out there and 'pound the pavement', so to speak.
last of course, is USTA.