I got a box of aluminum pop rivets from McMaster Carr Poppack100 AD610AB5203, Grip Range .501-.625" hole size .192-.196", I've still got most of the box maybe 80 left, I might be persuaded to part with some or all, it takes about 20 per side. These were recommend by Dan [MENTION=57920]racerxxx[/MENTION] and worked great. I'm not sure what I paid but if you're interested I'll look it up.
I'm pretty sure the originals were aluminum because they drilled out real easy.
Lou