Duncan Head, Armies of the Macedonian and Punic Wars, 359 BC to 146 BC (Wargames Research Group 1982)
This is the major extant western source, Megasthenes and Arrian:
link
The Arthashastra by Kautilya is the major contemporary written source, but was written after 200BC.
link
Check University libraries for these.
I can't say they are unbiased source material, but it's a start.
Sarva Daman Singh, Ancient Indian Warfare, (Motilal Banarsidass Publishers 1997) Mostly covers "Vedic" or earlier material than this period, and a bit hard to read. But full of juicy details on weapons and armour, some too juiced up.
Radha Kumud Mookerji, Chandragupta Maurya and His Times, (Motilal Banarsidass Publishers 1999) Compares the Greek and Indian surviving texts of this period.
JJ
gets medieval.
