Buying Accounts or Smurfs

Yes it is against the rules (and will result in the accounts being permabanned), and no nobody knows any sites to get them.

http://na.leagueoflegends.com/en/legal/termsofuse

#1.4. Can I share or sell my account or login credentials? (No.)

When you create an account with us, we require you to select a unique username and password (collectively, your “Login Credentials”), which you’ll use each time you access the Game. You can’t share your account or Login Credentials with anyone. You can’t sell, transfer or allow any other person to access your account or Login Credentials, or offer to do so. You’re entirely responsible for maintaining the confidentiality of your Login Credentials. Please notify us immediately if you become aware of any breach of security, including any loss, theft or unauthorized disclosure of your Login Credentials.