Hi Stuart, the V.I.N. plate brass rivets were never supplied as a part, plate was attached in Japan using local rivets. To attach the V.I.N. plate after painting or resto work, most times an aluminium pop rivet is used. If you are after OEM finish (to satisfy the Rivet Counters) an option could be to check out snap head rivets from a fastener supplier that may have small brass snap head rivets. To fit the snap head rivets the steering stem has to be removed (unless the frame is bare after painting) so a backing-dolly can be used inside the steering stem. Some gentle sanding and polishing may be needed to make an exact copy of the original rivet. Steering lock cover plate rivet is not the same as V.I.N. plate rivet. Suzuki used to supply the steering lock set with a new rivet however, not sure if that is still the go. Check with Steve at Mick Hone spares.
Cheers.