Mil-Spec nickle plated 1/8" diameter Tublular Rivets.
Check the length against your original and allow 0.129 inch for the clinch/roll-over.
A good length rivet for repairing original ramp flaps...
Williams - 07-6688-19
Check out which 1/8 inch rivet washer you want - 0.032 or 0.060 inch thick.
Photo is just a regular rivet, not this one...