The best way to get into catch riding is to contact the local trainers (or better yet, have your trainer contact them). Catch riding is difficult to get into unless you already have a name for yourself, so it's best if a reputable professional can back you up in your skills until people in the area know who you are. And even still, they may have a list of riders already in the barn who would be dying to show a horse for someone.
Also, are you over 18? You can't show in pony divisions over 18 y/o.
And I don't know if you want to keep catch riding in college, you may want to look into the rules of your equestrian team. I'm pretty certain most are VERY strict about being you being an amateur... which means you cannot get ANY sort of payment for riding/showing a horse (money, board, a hotel room, ANYthing).