Leveling up?

Question

I've beat N.
I know about the sports stadium
I beat Gamefreak in castelia city
I've battled Cheren in Victory road
I've beat Bianca in Juniper's lab
Where else can I go to train?
Also know about the E-4 rematch
(my pokemon are level 78-82)

Answer 1

You can battle Cheren evryday day at Victory Road.
You can battle Cynthia at the Villa in Undella Town everyday, from spring to fall.
You can battle the Gamefreak guy everyday.
You can go to the stadium everyday.
You can go on the royal unova ship everday in the evening.
Rematch the E-4.

Those are all the places left in the game that I can think of to train.

Answer 2

Repeat the elite four "x" times untill lvl 100 I guess.

Answer 3

You can challenge the E-4 again and they will have different pokemon at different levels.