You might try the following:
Mundane Astrology -
Mundane Astrology
Author: Michael Baigent, Nick Campion and Charles Harvey
Mundane Astrology - Astrology of Nations and States
Author: H.S.Green, Raphael, Charles Carter (this is a bit dated, though something of a classic)
Electional Astrology
Electional Astrology
Author: Vivian Robson - one of the few books devoted to the subject, again something of a classic.
Only Way to Learn About Horary and Electional Astrology - Vol 6
Author: Joan McEvers and Marion D. March
This one covers both horary and electional, Its qute a good series, and I have this particular volume.
You will find both branches of Astrology covered in volumes dealing with a range of Astrology - for example, Nick Campion's 'Practical Astrologer' but there is little directly on these two areas.
Hope these help