EDIT: I later saw you posted this in the 1800 board. Your post made it sound like you were talking about a 1500. If you are talking an 1800, never mind.....
The original solo rack for our bikes (goes where the passenger seat does) is no longer available, and commands steep prices used. It is small and curvy and more for looks than good function (only good for keeping things off the paint). It was made by Big Bike Parts/Show Chrome.
Some guys have modified another similar looking (and still available) rack to fit (there should be a thread here on it somewhere).
Custom World International (Quebec) used to make a nice larger flat rack that was much more functional, but I cannot find it on their website now. I'd call and ask (they may only speak French). Some American companies may sell CWI stuff, and be of some help (like Phat Performance). It was more in the $200 range. (And you have to be careful it doesn't contact any big aftermarket seat back.)
https://www.classiccruiser.com/products.asp?item=1460This was it. (good tie downs on the rack itself, instead of running bungees to the Valk fender struts and rubbing the paint).
The idea you might like for a solo bike, is to mount an aftermarket trunk (maybe with extra lights) over the rear seat area. But then the sissy and sissy luggage rack would probably have to go.
Also, the paint under the passenger seat was never as good as the rest of the bike, and you may find the stock pillion seat better at padding tied down loads than a puny rack. I used to tie down a big soft duffel bag across that Show Chrome solo rack, and the ends of my bag drooped and rubbed the bag lid paint pretty good (bad).
