This is a difficult bolt to find, but KC suggested I try a Fastenal store. They did not have any at the local stores, but the manager called a supplier, and they agreed to "sample" 4 bolts to me! So now I'm waiting on them to arrive.
My new throttle cables should arrive today or tomorrow. Unfortunately, it does not look like I'll have the bolts in time to get the bike ready to ride this weekend. I was hoping to get out for a little ride--maybe http://www.Head2Holt.com.
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Another HUGE thank you to Dean. Thanks also to Mike for his help. And of course thanks to you guys for your suggestions and to Ian for even offering tools and his skills if needed. Ian--sorry to hear about your stolen 636! Right out of your garage, eh?!