Make one out of a hacksaw blade, I made one for a banana patchbox that was a lot more complicated than the Investarms spring.
Heat it, bend it and quinch it in oil, it will work.
The spring I made the same way. I am pretty sure I made the lid and the catch spring; I put the box on backwards by mistake and messed up the lid spring in the process. I may have repurposed the lid spring but I definitely made the catch spring.


