How do you block your profile from people who want to add you as a friend on Facebook?

It appears that that is impossible - it's a compromise, you either add people you don't know as "friends" to grow your mafia, or you keep a limited mafia size and your privacy.

I thought adding Mafia friends to a limited profile would do the trick, but there is no limitation of any kind.

Would love to hear it if I am wrong.

You can change your profile to a level of private so that no one can search for you or block specific people from even being able to bring your profile up in a search.

You can "friend" someone to grow your crew and then "unfriend" them and keep your crew size.