hi ajt
The quickest (and not illegal) way to access peoples' names and addresses is to look at the phone directory. Of course some people do not have their number listed. Electoral roll would not be possible as data is confidential. Even if companies have such information they would not be able to release it to you for research.
Of course you'll need ethics approval for your research since you will be collecting data from people, and I assume it will be lots of people :-) When you prepare your application, you'll have more ideas where to find your sample :-) for example--if you were looking to administer questionnaires to say a group of nurses, perhaps you could approach targetted hospitals to speak to their Director of Nursing, or Matron, or whoever is in charge, tell them about your project (assuming it has been granted ethics approval to start) and they would then perhaps help you to find the sample of nurses that you need.
best of luck
love satchi