The Vintage Sport was probably the most flexible bike Big Dog put out. It was one of the reasons I got mine.
They had two seats, a stock fastback vinyl and a two up stitched leather. They had two types of quick release sissy bars, a simple short "grab rail" and what Harley would call a "medium" height one. Two sissy bar pads were available, a narrow medium and a wide medium- the narrow was vinyl. There was also a luggage rack kit available that bolted on to the sissy bar. They had a quick release leather saddlebag system, and a bolt on windshield kit. There was also the standard tool bag and other generic stuff that would fit all their bikes at the time.
I'm pretty sure what they did was take all the Vintage Classic model bolt on accessory options and make them (except for the windshield) quick-release, so they could sell it as as a stripped down pro street rather than a cruiser- but leave the owner the ability to put all that stuff on for the long rides.
I did buy the windshield but modified the brackets and Harley quick release windshield hardware so that my windshield would be quick release as well.
I figure the reason all that's hard to find now is that if the bikes are running, the owners don't want to give any of that up! If the bike's gone, no reason to keep the old stuff around. It's probably not likely owners bought multiples of each item, or kept the accessories after the bike was gone.
Good luck in your search for stuff! I'd be interested to know how you fare. FYI, there's a "vintage big dog" area on the site that I think most of the doods here with older models keep an eye on.
Peace, Respect,
OHM