This is a complicated issue, but to answer your questions simply, the college does not have to approach you. Also, many athletes on NCAA gymnastics teams don't have scholarships, they are called "walk ons." There are some NCAA men's gymnastics that don't have any scholarships or full scholarship. For 99% of people, I think it's probably going to be easier to get merit aid for academics or something other than athletics - there's just more of it and much of it requires less of an "unusual elite ability" if you will. Some NCAA athletics are at schools where they qualify for tuition breaks as a result of their high school academic performance, or they have outside scholarships which are given based on a variety of traits.
You may have a chance at making an NCAA team by focusing a lot of effort on your best events to bring them up to a competitive level, since teams often have "specialists" who don't do all around. I am really more familiar with womens gymnastics though.