I think you need a specific tool to put in a rivet. I assume a lot of people who have these cages must have run into this same problem. Maybe I'll post it on the enclosures forum for more exposure.
I have an old one that is not "feeder proof" because it never went together nice and tight but I have never had trouble with the rivets loosening up. I don't think it is aluminum as it is quite heavy. It was from Chris at reptilehaven about 5+ years ago. I use it for my wild silk moth rearing in the summer and cocoon storage in winter and it has proven indestructible! I think the aluminum, being soft, dents a bit where the rivet is attached and adds to the problem...