I don't think there is a Trainer with a Finneon, but there is a trainer with a Lumineon somewhere.
You can find a Finneon on Route 205 South, Route 218, Route 219, Route 220, Route 221, Canalave City, the Valley Windworks, and the Fuego Ironworks.
You can also find a Finneon in Iron Island if you fish with the Good Rod.
Route 222 or 224.
It is finneon!
Level 30.
When you surf up to Sunny shore city, there will be fishermen trainers. The first trainer you see will have a Lumineon at level 38, the evolved form of Finneon.
Canalave City use good rod.
Route 222 or 224.
You can't catch it but you can see it. A trainer south of victory road has it.
In Pokemon diamond, Pearl and Platinum you can see the evolved form of Finneon, Lumineon, on Route 223 in a trainer battle. The trainer who has a Lumineon is called Miranda. In Pokemon Platinum the trainer Cassandra also has a Lumineon.
Finneon will evolve into Luminneon at level 31.
You have to get a finneon,and evolve it yourself
The only one I can remember is a female swimmer on route 220. You can usually find lots with the Good Rod though.
It is finneon!
route 218 (good rod)
it evolves at level 20
you raise it to level 31
Level 30.
Sorry but there isn't a trainer with a bagon in platinum.