You can get all your screen sizes with code like @Carl.Gould suggests in the other thread you posted in:
from java.awt import GraphicsEnvironment
env = GraphicsEnvironment.getLocalGraphicsEnvironment()
for i, screen in enumerate(env.getScreenDevices()):
size = screen.getDefaultConfiguration().bounds
print "Screen %i is %dx%d" % (i, size.width, size.height)
Output when tested in script console with a couple monitors:
>>>
Screen 0 is 1366x768
Screen 1 is 1920x1080
>>>