You might also want to check:
1. The Hospital Information Desk
2. The Health Sci Library Information Desk
3. Both William's and the Tim Hortons in the building(s)
4. Security services as Sara mentioned
http://security.mcmaster.ca/lost_found_report.htm l --> that's how you file a lost report
I lost my wallet on Thursday and somebody turned it into the William's cafe so you never know where a lost wallet will end up. I hope you find it!