You may have trouble finding Eiscue in Pokémon Shield and Stonjourner in Pokémon Sword.
To get both of them, you'll need to make exchange between the two games.
Where to find Eiscue and Stonjourner
Go to Route 10 to find one of them more easily (depend on your version). Be careful, this is a random encounter. You'll not see it directly in the Tall Grass like other Pokémon, but via Exclamation Points (non-overworld). Be careful, you only have a 2% chance of running into it!
Another solution is to go to Lake of Outrage (Wild Area) when it snows. Your chance of seeing it will then be 5% if it's a snowstorm (still non-overworld).
Both forms of Eiscue are only related to his Ice Face Talent (The ice on his head takes physical attacks and its destruction changes his appearance. The ice cube re-formed when it hails.) So there are no two forms to catch.
Here are all the steps to transform an Milcery into a rainbow Alcremie in Pokemon Sword and Shield.
