original sprocket will let you go about 50mph. that is why everyone is changing them.
'old bike barn dot com' has a sprocket for cheap. the
tooth count is a personal decision. i went with a 38t. yours will have a number
stamped on it if you like how it goes use the same.
then go to your local honda dealer and get the bolts. here are some #s.
i got these from dandaman. very happy with the parts he recommended.

sprocket= JTR27938t. for a 38tooth. the last #s are the tooth count. (36t,or??)
bolts= 90128-382-670