you'll have to drill the broken bolt out
1st find or buy at a hardwear/auto store a drill piece for drilling metal thats the same size as the broken bolt then drill it out
you'll have to buy a re-threading tool costs less than $10 or some hardwear shops can do it for nothing (just take the top triple clamp off first

)
then buy a the bolt either from a honda dealer or just buy a similar bolt from the hardwear store