1. Route 39: This is the most common location. It's found near the entrance to the Ice Path, inside a house on the left side of the path.
2. Blackthorn City: You can find another Ice Stone inside a house in Blackthorn City. This house is located on the right side of the city, just past the Pokemon Center.
Important Note: Both of these Ice Stones are rare items, so you may need to reload the area multiple times to find them.