If your bike is still under warranty and the OEM part fell out during typical/normal operations, I would be raising h*ll with the dealership you bought it from. There's no telling how many other bolts on the bike are improperly torqued. If you don't want to waste your time on that, take out one of the remaining bolts, and go to your local mom and pop hardware store and ask them to match that bolt. Not a big box store, something like Ace Hardware or the like. They have bins of every bolt imaginable, and will sell them at less than $1 each. The sort of size you're looking for I have to think would be under a dollar. Even if it were $2 for a single bolt that's much less than shipping would be.
You could also contact your local dealership and see if they have any laying around.