Probably best to count the links on your current chain. The 550 has a larger rear sprocket, so a chain for a 550 might be longer than needed for a 500.
I don't find it listed anywhere. I assume you don't have the facilities to cut a longer chain to proper length. Maybe if you call the Honda dealer under the guise of purchase, they may look it up and be able to tell over over the phone the correct length?
Cheers,