Cotter pins, make sure the head doesn't strike anything. try to orient the smooth curve of the pin to the spring pressure.. You can use softer brass/copper pins for an easier install.
Screw threads will eat the roller, a flathead shoulder screw might work though.
The big no-no is bending an arc into the rivet; = bent axle stub. They bend easy. Check, double check, and check a week later that the rollers actually roll and NEVER hang up and slide, even slightly.
Buy three rivets and two rollers for each side too. Breaking a new roller is almost as common as a warped rivet. (These are pocket change priced, literally)