Without trying to be pedantic I think the reason why you see the moon larger is because it's much closer to the earth than the sun, and because it's on a different azimuthial angle (lower in the horizon basically). As far as smaller moons I haven't seen any specially made for GWX so I would suggest you get any one you like from
http://u-boot.realsimulation.com/. Just make sure you enable it using JSGME to be on the safe side
