You don't get Exp share in a city but do the following to get Exp share, first go to fuschia city and go to the right there is a big building enter it and go upstairs there is a scientist talk to him he will give you Exp share if you have 50 species of Pokemon in your pokedex.
Castelia city :)
go into one of the houses and talk to the man show him your basic Pokemon and he'll give you an exp. share.
You receive exp share from the president of the Devon corp after delivering the letter to steven, or you can win one from the lottery at lilycove city it is second prize.
An oak aide in a big building east from fuchsia city has exp share.
you have to fill up your pokedex with over 50 different kinds of Pokemon then find professor oak's aide he will be in that thing were you transfer from city to city, the top of that building.... with the security guard...... if you have filled your pokedex to over 50 Pokemon he will give you an exp. shareoak's aide will be in the transfer between route 15
Professor Rowan's assistant in Eterna City just before the cycling road. Enjoy your Exp. Share! :)
Go to gamefaqs trade board and you may find someone willing. The soothe bell is available in nimbasa city, see video. I've linked a video for the exp share also, this can be gotten in castelia city
You can find the Exp. Share in Rustboro City or in the Lilycove Dept. Store.
Castelia city :)
An oak aide in a big building east of fuchsia city has exp share you need to record 50 Pokemon in your pokedex and show him that, he gives you exp share for your accomplishment.
An exp share allows you to share exp with another Pokémon. You can get it in Pokémon Diamond Pearl and Platinum near Eterna City.
Eterna City
in castelia city/ icirrus city
After you deliver Mr. Stone's letter at Slateport, go back to Rustboro City and talk to Mr. Stone at the Devon Corporation (Top floor). He will give you an Exp. share.
From proffeser Oak.
Exp. Share (2) can be found in Castelia City and Icirrus City.Castelia City: Battle Company,top floor. Can be obtained by defeating the janitor.Icirrus City: Show the man your Pokemon in the Pokemon Fan Club. If you trained it well enough, he will give you the Exp. Share.
Trade the red scale to mr pokemon