So I just gave the exam last week.There's only a small gap between what I did and wished I did. Pull out the Pol Sci syllabus and follow with me. All books marked * are in the syllabus readings. Here's my recommendation:

Paper 1 — Part A
Western Thinkers from *Judd Harmon.
(I got it from Urdu Bazaar in Karachi, did not find a PDF)

Islamic thinkers from *Rosenthal.

Paper 1 — Part B
90% of this is a standard Pol Sci intro course BUT with Islamic elements. So I just used the Mazhar-ul-Haq Political Science book. It's used in government colleges so you'll find a copy anywhere. It's pretty solid as an introduction.

If you want to build more depth/have more time, study the same chapters in Political Science by Andrew Heywood, for review. It doesn't have the Islamic elements though.

Paper 2 — Part A and B
Okay, so this is important.

The first topic in Part A and the first in Part B deal with the "Comparative and Analytical Study of the Political Systems" of 9 countries in total.

I took Constitutional Law as my optional subject, so I studied 5/9 of these + Pakistan, which is also in Part B.

I can't speak to how scoring/easy Con-Law is, but it was a delight to study. People usually throw around that Pol+Con Law and IR+International Law are recommended combinations. That wasn't my reason, but the overlap did help.

Whether you take Con Law or not, I studied the Anup Chand Kapur book "Select Constitutions" and *Hamid Khan in parts. The first is available chapter-by-chapter here (it's a painful download) and the second is a little costly but at Oxford University Press.

Rest of Paper 2
In Paper 2 — Part A, the "Global and Regional" section is something you should study for Current Affairs and your Essay anyway. Just study topics from the Internet and any introductory textbooks. Google will get you more than enough recommendations.

In Paper 2 — Part B, section IV was all from Pakistan Affairs, section V was Hamid Khan* and Pakistan Affairs, and section VI (for me) was based on Current Affairs, the newspaper, general knowledge.

Good luck!