Large units of mostly Seleucid or other "lesser" infantry units are hard to come by in the world of 28mm.
I like the suggestions above. The Magister militum figures are a bit old but useful. You are just going to have difficulty with finding off the shelf figures in 28mm (or even ancient 25mm Naismiths or Minifigs) that fit the AMPW mold.
My guess is that the so reported 10,000 Arab troops from tribal allies were mostly thureophoroi. Many may have had Hellenistic gear. Given the lack of battlefield reporting of any missile fire effectiveness, I doubt a large percentage were devoted archers, slingers' or javelinmen.
Maybe a thousand or so of pure lousy quality missile skirmishers, and if one wishes an archer block-- but less than the foot javelin/spearmen probably (given their lack of ability vs the Thracians opposite) open order.
The issue is always this contingent is large and needs lots of figures to fill out (if Antiochus' army is 73,000 men then this is 1:7th of the total). Sadly they are mostly useless troops, exactly the kind of units that gamers don't want to waste their time with. (Which is why the more thrureophoroi you make, the better, because these can be used more often as militia or garrisons).
One place to go is plastic Numidians. which you can convert. Spikey beards are very doable:
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These Footsore figures are very useable:
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