http://gamut-was-taken.github.io/Not too sure on what HP Lando runs, so I'll do the maximum damage possible.
Weavile is one, albeit very obvious switchout to LandoT. With very slight damage on it before, a -1 Ice Shard OHKO's after rocks, so you don't have to worry about the scarf on it. Like I say, it's pretty obvious that Weavile will have Ice Shard, and it will likely be scared out, but it's a check atleast!
-1 252 Atk Life Orb Weavile Ice Shard vs. 0 HP / 0 Def Landorus-T: 239-286 (74.9 - 89.6%) -- 18.8% chance to OHKO after Stealth Rock
I'm fairly sure there are plenty more too!
Edit: As we're here, are there any ORAS damage calculators? I'm using this one and it still only goes up to XY!