Tentacool can be found in the water all around the route's near sootopolis city, mossdeep city and pacifidlog town.
Use Surf on Route 205 and you'll easily find a Tentacool.
I don't know where you can find a trainer with Tentacool, but you can easily find it surfing on Route 205.
it is Tentacruel
In RSE you can find Tentacool on Route 103.
You can get it from a trade, the GTS, or find it possibly in the waters between the Fight Area, the Resort Area, and the Rest Area. You can find tentacool by just surfing just about anywhere. Or, using a good rod or old rod.
if you have surf then anywhere with water
Tentacool evolves into Tentacruel at level 30.
you can't you have to catch a tentacool then it evolves at level 30.
With the old rod you have the lovely selections of Magikarp and Tentacool
Tentacool evolves at level 30 in all games.
Tentacool evolves into a Tentacruel at level 30.
Tentacool evolves into Tentacruel at level 30.