I know you’re looking for evolution lines, but this Bouffalant has a connected story artwork with this (snowy) Natu that might be worth picking up for that reason. 
Here also some similar threads to perhaps get inspiration from:
- Favorite Winter/Holiday/Christmas/Snowy Day Card Arts?
- Japanese Autumn/Winter Pikachu Promos
- Favorite Fall Themed Card
A nice one I saw in that thread to add as evolution line would be this one:
Or this Flaaffy instead, since you said ice/snow, not Winter/Christmas:
Too bad there isn’t a snowy Ampharos to go along with it.
Greetz,
Quuador