Magnets? Best kind?

So I am reviewing a fix on some armor I've made previously. I've heard of people using Magnets to secure armor pieces or visor pieces or pieces of props and costume together. Can anyone recommend a strong enough magnet to hold two pieces of 6mm plastic together and where I can get them at or at least where to find them? I've tried some at the the hardware stores and those don't seem to be strong enough. And if you've used them before can you post a link to what you've used them on so I can see the example.
Much appreciation for RPFERS!