The world (Google) is really your oyster.  I have done something similar recently and created 50+ posters in no time at all.

What I would suggest is that you tailor part of the notice to your organisations own visual identity (or create one for this process).  Perhaps with different templates for different messages. This builds on the 'achoring and adjustment' heuristic (mental short cut) so that viewers recognise the type of information being communicated and associate it with a formal company SHE message without conscious thought.  

Remember pictograms are key and use of the Signs and Signal Regs can aid this.  I would place them, where possible, in areas that are frequently looked at without specific effort such as at point of use, sinks, toilet cubicles and above urinals etc.  Noticeboards tend to very quickly get bypassed unless you find another reason to make them a destination.

If you do take open access images from the web, I always make sure it is clear where the source information comes from.

Edited by user 13 January 2020 13:48:43(UTC)  | Reason: Additional text

Also have a look at: businessballs.com and health and safety for beginners https://www.healthandsafetytips.co.uk they have a good spread of freely downloadable stuff.