Surskit are mostly found in the tall grass. They rarely appear, but keep looking. After you defeat the Elite Four, TV Pokemon News will tell you that either Skitty or Surskit have appeared in swarms on their routes.
It's quite a challenge to raise and train a Surskit into a Masquerain. Mine is at Level 45. Take my advice and use a Macho Brace on it. It's stats aren't stellar, but it could increase if Macho Brace is attached.