How can i obtain baptismal record from mexico on my ex husband if he does not remember the church or city?

he was born in mexico around 1965 to 1971 and i don't know what church or city in mexico he was baptized in. I need a copy of this record to get an annulment through the church so i can get remarried to someone else. My ex husband got remarried already in mexico, in the catholic church ten years ago.