I could only find this question for Black/White but not for Black/White 2, and I'm starting to get really frustrated. Can I get the Soothe Bell before the third gym, because I want an Umbreon? Help would be appreciated!
In Nimbasa City:
The house directly above the Pokemon Center has a lady inside that will determine how happy your lead Pokemon is with you ... go to second floor of the house next to that and talk to the Socialite and she'll give you a Soothe Bell if your lead Pokemon is at least moderately happy with you.
BLeh
I've seen people just say above the Pokemon Center, but it's above the Pokemon Center and to the right one house. It's above the fighting house next to the Pokemon Center on the second floor. The old lady in purple/pink with give it to you if you show her your Pokemon that likes you (this is in Nimbasa).