Vespas went through a lot of detail change and it depends a lot on the model of scooter that was used, so do your research carefully, and remember that 1966 was an important year for Piaggio...their factory was flooded and things changed after that.
I know that there is a 50cc Vespa in the 1/24 scale Tamiya Campus Friends kit. I also have a 1/8 scale 50cc Vespa kit, and I don't remember the manufacturer (I think it may have been Imai, but I am unsure). These are the small frame Vespas.
My guess is that the military used the large framed scooters which had 125cc, 150cc and 160cc engines and I don't know of any kits. There may be diecasts out there.
I am interested in seeing what else is out there.