+1 on TPO Parts, but to the OP, be warned as you will purchase more than just a side stand bolt when you see what else they have for sale.Wow, you snapped it!? Nice work!!!
For the oem part I know most places online like pro-italia et al have a catalog for your part and you order off them but I'm not sure they'd have that particular part in stock.
What I do know is that tpoparts.com have a nice titanium one for $19.99 and you can get the bolt and nut for $29.99.
No, I'm not affiliated with them in any way but they do awesome titanium parts and its worth checking out their website. Bought quite a few pieces from them.
The stand bolt is a 'special', and not available from a general selection.My local ace hardware has a real nice stainless nut & bolt section. It's always my go to place when I need something. Bring whatever pieces you have and it's easy to find what you need. I always expect that I will have to make something work and to my surprise I find an almost identical piece of hardware. Good luck I'd try Gotham but I'd assume most get packaged together with the stands they sell.