If you are a member of a congrigation and you know what city you were baptized in, you can tell the parrish center and they can contact your original parrish for you. Believe me, the Catholic Church keeps paperwork. With a couple of phone calls they will be able to get it for you. I know because I had to do the same thing, only my original parrish no longer existed at all and they had to track down my certificate! Took a couple of weeks, but I got it. Best of luck!