You can find Lumineon on route 221, if you have a super rod.
Finneon evolves into Lummeon around lvl 34
You will need a Super Rod for this. If you do not have one, you need the National Pokedex. Go to Jubilife City and go towards canalave. When you us Surf, use your super rod. You might battle a lumineon. If not, repeat until you catch one. Bye!