There are 2 approaches to finding employment agencies - directory search and/or web search.
Web search: Use your favourite search engine to find "employment agencies" and add a location. For example, your search might say
"employment agencies" +barrie
There are many Career | Co-op | Field Placement resources on the Student Portal.
Select the "Student Services" section.
Select "Career | Co-op | Field Placement"
Select "Looking for Work" and scroll to the section on Employment Agencies.