You can apply in British Council and AEO in Pakistan for the IELTS.
AEO offices are situated in Islamabad, Lahore and Karachi. You have to visit the offices to get form or download it from their official website.
British Council offices in Islamabad, Karachi, Lahore, Multan, Faisalabad and Hyderabad offer full testing services on a regular basis. It is not required to attend a preparation course though it is a good initiative to practice thoroughly ahead of time.
You can get IELTS Registration Form from Standard Chartered Bank or download from the British Council official website.
You have to attach a clear photocopy of your valid Computerize National Identity Card or Passport, two colored passport size photographs without eye glasses (not older than six months) and your payment deposit slip of Standard Chartered Bank (Demand Draft in favor of respective British Council office). Banks details where you can deposit fee given at the end.