I've seen people glue them on, but I don't know how well they stayed attached. I know you can buy a snap set at a craft store, it usually consists of a plastic base, with a metal pin used to hammer the tab in the center of the snap down... they're pretty cheap. I think around $7 if I can remember correctly.
I've had no luck with those snaps. The sew-on kind are better. I think my problem was with the tool itself, maybe if it wasn't the cheap plastic. Never could get them to line up right and it was a disaster.
As far as putting it on your armor, a good glue should work. I think I used superglue. If you can rough up where you're going to glue it, it'll help take hold. If it's plastic, you can make little cuts to help it cement in better.