Here are the locations for the Eevees in DX!
Eevee: Joyous Tower, Starter/Partner
Vaporeon: Grand Sea, Far-Off Sea, Northwind Field, Silver Trench
Flareon: Fiery Field
Jolteon: Lightning Field
Espeon: Murky Cave, Remains Island - Strong Foe (Shiny Capable)
Umbreon: Fainted in Dungeon, Mystery House
Leafeon: Fainted in Dungeon, Mystery House
Glaceon: Fainted in Dungeon, Mystery House
Sylveon: Fainted in Dungeon, Mystery House
Should you have an Invitation, then you can enter the Mystery House. Within this house, you'll get a variety of items including Reviver Seeds and Max Elixir. In addition to that, if you speak to the Pokémon in the Mystery House, they will be wanting to join your journey. These Pokémon are ones that don't normally appear in the dungeon but will often feature the same theme as the dungeon as it is such as typing. For example, you could find Lapras in Northwind Field as it matches the Water and Ice motif.
According the the information I found, you can randomly get the Eevee's listed above ^ sometimes in a Mystery House. Since it's random, there's not a specific house. HOWEVER, certain Pokemon tend to spawn more commonly in houses in locations where it matches the type.
TL;DR you can only get certain Eeveelutions randomly by Mystery House or Evolution. Try to look for houses in areas that fit the theme of the Eevee you're looking for-- like snowy places for Glaceon. Good luck!