How many ribbons do you need to get into the ribbon syndicate?

you need 10 different types of ribbions.

10

at least one of your Pokemon need a master rank ribbon from a contest in hearthome

you need ten ribbon to be a Pokemon diamond pearl

If you haven't yet entered the Hall of Fame, you must do that first, then go to the outskirts of Snowpoint City and ride the boat. Make sure you have the National Pokedex(see 150 Pokemon, enter Hall...