Assuming there is a rear carrier on your scoot you can make your own top box rack:
I made my own rack out of 3/4" plywood for both my GV 250 and DT 300. First, I bought a new top box (27" by 13") on ebay for $49.95, postage included from an outfit in Pomona, CA. The box comes with a sturdy plastic mounting bracket that allows quick release of the box. Interestingly, it's the same exact Chinese box that Saddleman sells for $200, but with their logo on it. I traced the outline of the provided mounting bracket on the plywood, cut it out, sanded the edge, sprayed it flat black, bolted it to the rear carrier, countersinking the bolt heads in the plywood to maintain a flat surface, then bolted the mounting bracket to my rack.
I believe that "Warning, 5 Kg limit" on the rear carrier is nonsense, Kymco's legal department attempt to avoid law suits.