I needed one recently and asked at the dealer parts counter. They referred to it just as a "small Suzuki rivet" and said there is mainly two sizes. $3 and 30 seconds later he gave me a few, exact match. Worth a try if your at a dealer.
I took my plastic push pin out of the side covers under the seat and installed a clip nut in its place with a button head screw so now it's just pull the screw out and remove the side cover no more push pin to mess with or worry about breaking on me.