The National Safety Council is a great one. I found this one to be useful by J.J. Keller. They have a few more work safety topics the NSC doesn't. https://www.jjkellersafety.com/resources/safety-calendar

National Safety Council has a nice calendar of safety observance days/weeks/months. I use these to frame some of my monthly safety talks.
https://www.nsc.org/events/safety-observance-calendar