I finally found them in Demonis >.< Demonis apparently sells troops of every race (don't think I saw orcs though) .. except that it is very inaccessible ..
But yeah, if one is using a pure elven army, there's not much good alternatives.. since there are so many fire damage dealing monsters by this point of the game (demonis, dragons, etc.) ants and sprites are not viable.
Thanks for the tip on the waterscroll
