I can't offer a good suggestion for a replacement lock.
I can offer some suggestions about how to keep your well meaning gesture from backfiring and hurting you.
A University setting has a lot of different levels of interactions. There are chains of command that normalize the most common means of communication. Direct communication between student and the Director of Technology Infrastructure is not usually a common interaction. It is even less common when the communications consist of the student raising awareness of an issue and bringing a solution that will be implemented. By honestly trying to point out this deficiency you are raising awareness of two things:
- The equipment is locked with less than top of the line locks, but it is locked.
- You have been evaluating the security measures that have been put in place to protect university equipment.
The chances that they will focus on the first item over the second are not high. Be prepared for that.
Keep it short, keep it factual and non-emotional. Distance yourself a little by finding an article, any related article to reference. Don't walk in and cite only your own knowledge. As much as possible turn it into "I was reading this article, and noticed that what it was talking about was right in front of me". That will help lessen the impression that you were evaluating the security measures.
The article serves two purposes. It shifts the source of the report from a student to a presumed professional, they will take the news better this way. It also lets you hand them something that contains all the points you want to get across. It can be a printout or the url of a youtube video demonstrating shimming.
Security disclosure is difficult for anybody, it is more difficult when you have to overcome having bypassed normal chain of command and communication channels.
Good Luck!