Go to route 217. Find a Snover and capture it. Then level it up to level 40
Abomasnow is located on the Ice Lake by tackling 3 times.What do you tackle?I'm not sure, Serebii.net just said to tackle * 3. Maybe a tree? I haven't played this game yet.
if you have them, my guide for the games and I myself recommend using a team of: an Electric type, a Fire type, a Flying type, a Grass type, a Ground type, and an Ice type. level them up to about level 80-90 or so (Cynthia is going to be hard), then, if you have enough supplies (there's no turning back), restore your team's HP and PP, and don't forget to save. She'll start with Spiritomb. use your strongest moves, or kill it slowly with toxic. most of her team have only one or two weaknesses and know moves that trump the types that should trump them. When possible, surprise her by using type-trumping moves from a Pokemon that isn't the same typa as the move it's using.