It's a good question and here is the first thing I do when it comes up.
I go to partzilla and enter honda motorcycle and the year, if it's early, look in the list under bikes with no year. (by no year, they mean not shown in their main list)
Next go to the section that might show the part you need to check.
Find the part in the exploded diagram, get the reference number, (such as #5) look to the right to find it in the list.
Even if it's not available you can click on the part. That will show you the part's page and you can scroll down to see a list of every other bike that same part was used on.