Your best bet is chance. Go to the Pokemon mansion and talk to the owner. If he talks about evee, go to the trophy garden afterwards. Keep in mind this happens only after you beat the Champion. Search in the grass, an evee is most likely to appear. Keep searching until you find a female. Unless you save before talking to the owner, you have one chance he'll talk about evee. In other words, you can only do it once a day.
a jolly nature female
To my knowledge (not there yet) I assume eevee is male and evee needs to female to mate with ditto (as all pokemon)
A male and a female eevee
If you breed a evee you will get an egg when it hatches it will be evee this is a great way to get all the forms of evee.
Evee is given to you in Celadon Mansion.
Evee + Ditto in daycare
To get vaporion give evee a water stone.to get flerion give evee a fire stone. to get joltion give evee a thunther stone and that is all for Pokemon leaf fire and and water
go to the trophy garden south of hearthome speak to mister backlot and he will tell that an evee snogged him. go out to the gardens and catch your evee. you can get an evee from bebe once you have the national pokedex
You level up evee in eterna forest
EVEE evolves at level 15
with the interview at the beginning u have to select female and then get the answers as an eevee would so u can be 1
put it in day care with another normal type and hatch an egg(evee has to be female)