Actually, 12.9 is the top of the chart, but these are usually only available in socket head fasteners. 10.9 will work fine in this application.
You should be able to find a proper JIS flange bolt in the correct grade at, of all places, Autozone. They stock a decent selection of JIS flange bolts for Asian vehicles. (JIS means it will have the flange and the proper 12mm hex.)
The counter monkeys won't have a clue what you're talking about, so just stiff-arm them and rummage through the bolt display yourself. It's usually in the middle aisle.
The bolt you want will look just like the old one, except it will likely have a gold coating instead of the black stock coating.
2002 Suzuki DL1000 V-Strom, Dark Metallic Space Blue
1983 Suzuki GS850G, Cosmic Blue
2005 KLR685, Aztec Red - Turd II.2, the ReReTurdening