The obvious other example is in sports---is there any sport which has a professional league where a substantial number of amateurs are seriously competitive? I'm unaware of any. In fact, professional sports teams are enormously better than even the best amateur clubs.
I think you will want to look at the National Collegiate Athletic Association (NCAA). Specifically, take a look at football, basketball, maybe even baseball. I'm usually hesitant to call the college football and basketball amateur, but they are generally considered still amateurs. In the article below, 40+ athletes were drafted to the pros. Most of these draftees contribute to the team by the very next year, some star. Ohio State has had the most players drafted from a single team at 17. http://www.sbnation.com/nfl-mock-draft/2013/4/27/4275658/2013-nfl-draft-results-breakdown-college