I believe that Heatran is a good Scizor counter. It resists most of Scizors moves, such as: Night slash, Pursuit, Quick Attack, Bullet Punch X-Scissor and maybe some others too. Heatran can just attack back with a STAB Flamethrower. You just have to watch out for Scizor's Brick Break and Superpower. Since the scizor you're fighting against has a focus sash, then i would have to agree that stealth rock would help tremendously too. I hope I helped!