In NSW any owner is entitled to view the strata roll at the Strata Manager’s office, although there is a charge for doing so. First identify any spaces that are unused, then find out their lot numbers and then you will find the name and address of the owners on the strata roll.
However, bear in mind that while owners may not use their parking spaces themselves, they are aware of their value should they ever sell which tends to be more than the actual value of the car space.
And alternative may be to rent the space for an extended period.