As an aid to help in the creation of some of the many units for this scenario, I have made this index of all the different troop types that can be found in all the pictures and illustrations shown on the 1st page of this thread.
PICTURE INDEX
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Picture #1: Persian Foot Guards (starting on the right and moving left
.)
Darius III, = wearing a purple robe with the broad white Median Stripe in front.
Royal Spearbearer or Apple-Bearer = this shows an Hezaraptis or guard commander.
Royal Standard-Bearer = the flag shows a version of the Winged Sun Disk of Persia.
(All these figures are at rest, and so are not wearing any visible battle protection, but see picture #5 for how they would be dressed on the battlefield)
Picture #2: Persian Mounted Guards
Royal Kinsmen = Darius mounted bodyguard.
(Several satrap rulers also had their own Mounted Kinsmen Bodyguards, but they would not be dressed in the royal purple)
Picture #3: Alexander versus the Indians (starting on the right and moving left
.)
Indian Swordman = armed with a long sword and a blue oblong shield, rounded at the top.
Indian Bamboo Bowman = armed with the 2 yard/meter bow (a 2nd figure is kneeling).
Indian War Elephant = with 1 warrior with a spear and a driver armed with javelins.
Phalangites = all wearing slightly different variations of Thracian type helmets.
Picture #4: Mercenary Hoplites (starting on the right and moving left
.)
Hoplite with a Thracian helmet = the symbol on the shield is not a Greek letter.
Hoplite with a crestless Corinthian helmet = the symbol is a trident or the Greek letter psi.
Hoplite with a pilos helmet = and I think we all recognise the symbol on the shield.
Hoplite with an Attic helmet = this is the type of helmet worn by the Civ3 Hoplite.
(Mercenaries were a rough and ready looking lot, who would prefer to spend their pay on functional rather than fancy equipment).
Picture #5: Persian Heavy Infantry (starting with the figure in the foreground
.)
Kardaces = these fought at the battle of Issues, with a spear and crescent shield.
Spearbearer = this figure is wearing a Greek type cuirass and a polished silver shield.
Archer of the Spearbearers = also with a cuirass, these would form the rear ranks of the unit.
(To the left rear you can see a unit standard bearer, also with a polished silver shield)
Picture #6: Alexanders Light Infantry (staring with the figure in the foreground
.)
Greek Peltast = with an old-fashioned pelta type shield and javelins.
Agrianian Javelinman = the snake symbol on the shield is not a national symbol.
Archer and Staff-Slinger = the staff-sling was an attempt to increase the range and weight of shot of the standard slinger. However, it was not a successful skirmish weapon and soon disappeared from use (probably because its rate of fire was slow or for the long training time it took to use it effectively).
Picture #7: Thracian Peltasts (starting from the right and moving left
.)
Thracian with a Thracian helmet = in his left hand is a kopis, an alternative to a sword.
Thracian with a Thracian hat = the two-handed rhomphia was not used in Alexanders time.
Thracian with a pilos helmet = he carries extra javelins behind his thureos type shield.
(In the rear is an early Thracian with a pelta type shield)
Picture #8: Citizen Hoplites (starting from the left and moving right
.)
Various Hoplites with Attic helmets = these wore much fancier equipment then the Mercenaries.
Slinger with a kausia hat = some ancient slingers also carried a small round shield.
Early Thracian Peltast = with the usual javelins and early pelta type shield.
Spartan General = Spartans wore their head in long braids like their old Doric ancestors.
Musician with flute = these maintained a rhythm to help keep the formation in step.
(Most city-states allowed their Hoplites to display whatever they liked on their shields, with the exception of Sparta and Thebes)
Picture #9: Alexanders Heavy Cavalry (starting from the right and moving left
.)
Hvy Cav with an Attic helmet = this would be one of Alexanders Greek allies.
Hvy Cav with a Thracian helmet = these helmets were state issued in the Macedonian army.
Companion with a Boeotian helmet = the lance identifies him as a Companion.
Alexander without a helmet =
.a bit of artistic licence here; he certainly would have worn one.
Hvy Cav with a shield = more artistic licence; cavalry didnt carry shields in this period.
Hvy Cav with sword = he would be at a severe disadvantage; a spear would outreach him.
(In the rear you can see a mixture of helmets, with the Thracian type predominating. This is due to rich noblemen being able to afford their own equipment and not have to put up with the standard state issue helmet)
Picture #10: Persian Cavalry (starting from the front
.)
Scythe Chariot = formidable looking, but vulnerable to missiles and not very effective in battle.
Bactrian Cavalry = horse and rider wearing iron scale armour, the man thrusting his spear overarm.
Cappadocian Horseman = horse and rider wearing bronze scale armour this time.
In the background, various Light Horse Archers.
Note that although not shown, the Massagetai (a Saka or east Scythian people) who fought at Gaugamela looked very similar to the Bactrians.
And the Armenians, who are also not shown, would look very similar to the Cappadocians.
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I hope all this helps when trying to find out what various units looked like.

What I havent got is any pictures of all the many different types of poor quality infantry that the Persians frequently fielded. But almost all of them would be variations of the Civ3 Warrior and Spearman, with either a bare or Persian head.