About a Galatian king...
The Galatians were 3 tribes each with a chief. The leaders who led the Tribes into Galatia were Brennus( different one from the one who sacked Rome), Leonnorius and Lutarius. Over 200 years later one cheif, Deiotarus, defeated the other 2 and was acknowledged as "king" of Galatia. Amyntas was the last king.
I'd go with Deiotarus but you could be lazy and use Brennus since his name and face are already in the Game.
Also, maybe you could use the graphics of the Dacian Falxmen as a Thracian. After all a Falx is a bit like a Romphialla...
Dom Pedro II s punic wars pack has a slinger and some elephants. The slinger is a bit too big but maybe someone could resize it for you...