I still can't find this bolt in the ofical Honda online store or the usual Honda parts suppliers, but I did a search for the bolt by size, thread, and length and up pops, believe it or not, a listing by WalMart.com for a flange head bolt of the same size and grade for $9 with an ETA of June 7th!
https://www.walmart.com/ip/1-M12-1-...8416&wl11=online&wl12=575836038&wl13=&veh=sem
Guess I'll order one of these unless the local fastener outlets have the same thing in stock, but I'd have to wait until Tuesday to find out about the local guys. Oh, what the heck; I'll just go ahead and get one on order. I would never have guessed there would be a WalMart connection.
Now...do I need that thin washer for the back side?
BTW, Charlie the $480 mechanic used a hex head bolt with a washer under the head, so I think I need to change that bolt anyhow.
EDIT: just saw that the same supplier and bolt is on Amazon for $11.
https://www.amazon.com/M12-100mm-Flange-Small-Class/dp/B00N05XT4G