best option is always 'word of mouth' - that is, do you have friends, family, neighbours who have used, and recommend, someone they have taken their PC to in the past?
what about the telephone directory; YellowPages (or your local equivalent).
then there's the local newspaper; Classifieds or "Find a Tradie" or Local Services sections.
what about Facebook groups promoting local companies in your area?
and of course, just plain Google "computer repair shops in <insert your town here>"