If you're looking for Ghetsis, you can't find him. THe others, though, are:
Zinzolin- Cold Storage
Bronius- Chargestone Cave
Ryoku- Relic Castle
Gorm- Dreamyard
Rood- Route 18
Giallo- Route 14
In Pokemon Black/White Versions there is only Six Plazma Sages To Discover
He just comes to capture him.
The seventh sage is actually Princess Zelda. She is the Sage of Time.
The sage is located in Undella Town. To get to it, you need to go to the water and go up the waterfall.
Looker tells you that the last time N was spotted was riding on reshiram/zekrom.
You walk up and down route 14 and after a couple of minutes, you'll find sage.
The seventh novel in the Septimus Heap series is Fyre by Angie Sage.
Bennett White goes by Bennett the Sage, and The Sage.
After you have Looker arrest the last sage out of the Seven Sages, He should thank you and he should also tell about a boy who sounds exactly like N, who has been seen with a dragon pokemon somewhere far away... ^_^
White sage is called "ವೈಟ್ ಸೇಜ್" (vait sej) in Kannada.
You just have to find them. Sage 1 - Dreamyard, in a previously inaccessible area, Sage 2 - Relic Castle, Sage 3 - Chargestone Cave, third level, Sage 4 - Cold Storage, inside a container, Sage 5 - Route 17, on the westernmost island, Sage 6 - Route 14, you need 'Waterfall' to reach him, Ghetsis - Captured at the end of the main plot, but escaped and can't be found (until Pokemon Grey, perhaps).
go head to violet city and you must battle at bell tower. work your way up to the top and battle the last sage. you will see your rival there as well. and after defeating the last sage, he will show you a escape rope. use it then you may make your way to the gym. good luck! [catchable pokemon: gastly]