The count function you're looking for is SVar:X:Count$ValidExile Card where card can be any valid type string. You can check multiple zones with this function too by stringing zones together although I can't remember the exact syntax.
Edit: not in front of my PC and suddenly not certain of the syntax. It might have an underscore before the zone, so "Valid_Exile Card". Also, "TypeInExile Creature" with a space instead of point should work, but I think that method was deprecated recently.