If you have a good hardware store in your area try there, Take one and match it up. I have a True-Valu hardware store that has 2 full rows of every kind of nut and bolt and fastener you can think of,
Bite the bullet and pay the shipping, or find a local Fastenal store. I've have good luck there in the past for this type of thing.
FYI, several Ron Ayers type places had the proper bolt for between $1.08 and $2.29, but shipping cost was way out of line ($10-30).
Well, I'm thinking that having had the bike for nine months and 7k miles might just get me an "I'm sure it was there and tight when you took delivery". It's nearly a 100 mile ride to the dealer from my house, so I'll give them a call first. It's worth a shot.