Unfortunately the finger pull throttles shown above have not been produced for nearly a decade. The reason for this is that all newer model electric scooter and bikes use twist throttles or thumb throttles instead of finger pull throttles. Finger pull throttles were only used on the first generation of electric scooters and bikes. They were prone to breaking the first time the scooter or bike fell, and received many complaints of tired and sore fingers from having to pull on them for a half to full hour during a ride. Nonetheless they may be the perfect solution to your build.
The only possible solution that I can think of is to use a brake lever with normally off switch as the throttle, such as our item # LEV-35 which is available on this page: http://www.electricscooterparts.com/levers.html
However this brake lever may be too large and bulky for your application.
I'm building an electric mountain bike, and want to experiment with a electric lever action throttle.
I've tried twist grip and was not impressed with it on rough tracks.
I tracked down a few possable leads on http://www.electricscooterparts.com/images5/ folder
I'd appreciate if anyone could let me know if these products are still available ?