Old post but thought I'd add what I've done while I'm thinking of other options. I've had this setup for several years now and it works great. When I first got my scooter I worked at making it lighter and have less rolling resistance. Things I do to bicycles. I replaced steel parts with aluminum and replaced the stock tires with 1.5" Kenda high pressure tires. The smaller tires allowed me to install a short-reach side-pull caliper brake. The stock tires require a long-reach brake (I tried one) but the braking power is peer due to the reduced leverage. The trick to use the short-reach is the use of a home made drop bolt. These were used way back in the '60's on bicycles that were made for long-reach brake bikes to allow the use of the better braking of the short-reach version. Back then you could buy factory made drop bolts but those are long gone. You can make your own as I did. My current issue with this setup is I now live where the streets are very rough and my narrow high-pressure tires give a pretty rough ride. I'd like to go back to a more stock type tire but I need to find a front brake solution first. The front fork is a standard 100mm spacing. I replaced the steel front wheel with an aluminum one. The rear is 130mm and will not fit the front. I'm curious if you came up with anything? If I figure something out I'll post what I did.
A well-equipped bicycle repair shop should be able to weld or braze cantilever brake bosses onto the front forks so that v-brakes can be installed.
David Johnson