Where's a good place to train the following Pokemon: (Pokemon Diamond)?

Question

Magnezone, Yanmega, and Porygon.

(Magnezone is level 45, Yanmega level 33, Porygon level 18, I need to train them to level 50)

Please tell me a good place to train them.

Answer 1

give exp share to porygon and keep switching in battle between yanmega and magnazone or double battles any way the pokemon league

Answer 2

The pokemon league

Im not crazy

give a Exp. Share to them

Answer 3

for magna zone use a super rod in any water and you'll battle about lv30 - 50 gyrados and wishcash

train up yanmega left of celestic town, there are lv 27 machoke, meditite graveller

and for porygon go to solocoen town and use the vs seeker on the people above the town

thats what i do