Make sure that your bike has brakes on it first of all. Any USAT race will make sure that it has front and rear brakes. I would recommend looking on USAT's site as well as the sites of the events near you. There may also be a tri group at your local university. Most of the schools here at least have it as a club sport. You may also try looking into a tri coach in your area, they could at least set you up with a group. I know I recommend a ton of different groups here in Austin to people all the time. Lastly I would go have a chat with your local bike shop, they always have a finger on the tri community pulse if they want to succeed.