My memory is hazy, but I vaguely recall needing to buy the backrest to get the luggage rack that I wanted. Personally, I wished I could get the luggage rack without the backrest because it got in the way of my 46L top case.
I purchased the genuine Kymco accessories from my local dealer in Vancouver, BC. Where do you live?
The other wrinkle is that I gave away the factory grab rail that had the turn signals on it. My dealer converted the bike to the integral body-mounted turn signals like they do overseas for the previous owner.