Riding a 2009 R1200gs
Join Date: Aug 2015
Location: Quebec, QC, Canada
One thing you can do, remove the bolt next to it, check if it can be used (you'll see at the same time if you need a longer/shorter one) then bring that bolt to the store.
Most of the hardware/home improvements stores don't have a lot of metric fastener, you might not find stainless, get a regular one, then change it when home.
Proud owner of a 2009 R1200GS....