how are these units appearing on the map? are they being trained? is so, you can do this:
event: [player-owned unit event]
a unit owned by player <x> finishes training a unit
condition:
[unit-type comparison]
unit-type of trained unit equal to <some unit>
[integer comparison - number of units in region]
number of units in playable map area of type <some unit> equal to <x>
action: [game - victory]
game - victory .....
if this doesn't fit your needs, then do this:
event: [unit enters region]
a unit enters playable map area
condition:
[unit-type comparison]
unit-type of entering unit equal to <some unit>
[integer comparison - number of units in region]]
number of units in playable map area of type <some unit> equal to <x>
action: [game - victory]
game - victory .....