since it is probably easier for you to search online and email, go find them
http://seniorcare.com.sg/product-category/mobility-aids/motorised-mobility-scooter/
email them directly for mobility scooter when i was in singapore, i used them because of their prices. do note that singapore by and large, is quite friendly for us to use mobility scooter or wheelchairs.
most newer hotels, buildings have wheelchair ramps for mobility scooters, electric wheelchairs etc.
the pavement they are now trying to retrofit to ensure level moving from 1 place to another.
however, at older buildings and streets, its really horrible. i have to depends on friends to help out.
rest assured all the main tourism places, like the zoo, bird park, senotsa, the large hotels, gardens by the bay, marina sand, are all quite wheelchair friendly. you will love it there.
i have to mention gardens by the bay as it is quite a joy to be there for my grandparents who need mobility scooters.
enjoy singapore!